Answer:
7.
![x=3](https://img.qammunity.org/2020/formulas/mathematics/middle-school/jmja0xwsmt4jtrinnsn2lhtcie4am0nxwn.png)
8. l=11cm and w=7 cm
9.
![x-5\ge12](https://img.qammunity.org/2020/formulas/mathematics/middle-school/ailnvzl0or9e7pz8x3kk1p11cxjiuguikj.png)
10.
![(x)/(3)\le15](https://img.qammunity.org/2020/formulas/mathematics/middle-school/87h02gx70yoggsim458rtp2uwx5k05nks3.png)
Explanation:
Question 7.
The given expression is:
![12-3(2x+1)=7x-3(7+x)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/echvcx2wv6zah0y5l4uitxx26zi0j5rdxx.png)
Expand the parenthesis using the distributive property:
![12-6x-3=7x-21-3x](https://img.qammunity.org/2020/formulas/mathematics/middle-school/55zubnt6bmcxm70noiz33ll4d1qy1shqf0.png)
Group similar terms:
![-6x-7x+3x=-21+3-12](https://img.qammunity.org/2020/formulas/mathematics/middle-school/vfsr8dpl2rwmkdw7szmhos6f87qqsfop32.png)
Simplify
![-10x=-30](https://img.qammunity.org/2020/formulas/mathematics/middle-school/vyf71x19wbz09eh4qphhrdb5i6oqfafqw2.png)
Divide both sides by -10
![x=3](https://img.qammunity.org/2020/formulas/mathematics/middle-school/jmja0xwsmt4jtrinnsn2lhtcie4am0nxwn.png)
Question 8:
Let the width of the rectangle be;
The length of the rectangle is
![l=w+4](https://img.qammunity.org/2020/formulas/mathematics/middle-school/p9korkfvwpjo4y917usqkqvhp8uzh205ir.png)
The perimeter is given as:
![P=2(l+w)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/iuzrgc5ydahb9ojuqi0cm1ha7m7zobnpkl.png)
Given that the perimeter P=36, then:
![36=2[(w+4)+w)]](https://img.qammunity.org/2020/formulas/mathematics/middle-school/ej08z66y44icuhtfm6unz80urwwfpvacvd.png)
![\implies 36=2(2w+4)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/8pqupqh5jfeg2moa3vp5f50dkx7lwvrjds.png)
Divide both sides by 2:
![\implies 18=2w+4](https://img.qammunity.org/2020/formulas/mathematics/middle-school/icwzagwczv6a5jdux6r778xik4y7052e79.png)
Subtract 4 from both sides:
![\implies 18-4=2w](https://img.qammunity.org/2020/formulas/mathematics/middle-school/iv6k73o80gfrvh7i8z8e2wc8gyp9kyku5o.png)
![\implies 14=2w](https://img.qammunity.org/2020/formulas/mathematics/middle-school/djfkx6wy0tq616hotkjpf2tklzi8c05t2w.png)
![\implies w=7](https://img.qammunity.org/2020/formulas/mathematics/middle-school/dlmqt7lkajvv8g4png0yrxrjebaeswusax.png)
The dimensions of the rectangle is: w=7 cm and l=7+4=11cm
Question 9
Let the number be x.
"5 fewer than the number" is written as
![x-5](https://img.qammunity.org/2020/formulas/mathematics/middle-school/9emoqjsgd118oanpemcwmldx3q7yrbe7hu.png)
"5 fewer than a number is at least 12" becomes
![x-5\ge12](https://img.qammunity.org/2020/formulas/mathematics/middle-school/ailnvzl0or9e7pz8x3kk1p11cxjiuguikj.png)
Question 10:
Let the number be x.
The quotient of a number and 3 is written as:
![(x)/(3)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/h8iro1cwpbavyhti4njsfhn1urx3ivax5r.png)
The quotient of a number and 3 is no more than 15 is written as;
![(x)/(3)\le15](https://img.qammunity.org/2020/formulas/mathematics/middle-school/87h02gx70yoggsim458rtp2uwx5k05nks3.png)