Answer:
5a) x=40 using the formulae for perimeter of a rectangle p=2(l+b)
120=2(l+20) factor out and you have 120=2l+40 make L subject of formulae then you have 2L=120-40 so L=80/2 L=40cm.
(5b) use the same procedure p=2(l+b) then L=250m.
6a) since both area and perimeter are give then using p=2(l+b), 20=2(L+B) so (L+b)=20/2 therefore (L+b)=10
Now introduce the formular for area which is A=L*B 24=L*B then making L sub of formular L=24/B substitute into (L+B)=10 then u have 24/B +B =10 find LCM you then have 24+B^2=10B this becomes a quadratic equation B^2 -10B +24 =0 solve and you have B=4 or 6. Substitute into (L+B)=10 to find L. L= 4 or 6
6b) use the same procedure as 6a.
L=2 or 12 and W =12 or 2