Answer:
Part A)
![86=2(x+22)](https://img.qammunity.org/2021/formulas/mathematics/college/5wzvdm7518h9p7d5fsc8i6wmgupwcjhdzn.png)
Part B)
![l=26\text{ cm}](https://img.qammunity.org/2021/formulas/mathematics/college/qwd6ukyka9rg9ig0o4undsgx5w3kg2jm50.png)
Explanation:
We know that the rectangle has a length of (x+5) and a width of 12 cm.
Part A)
Remember the formula for the perimeter of a rectangle:
![P=2(l+w)](https://img.qammunity.org/2021/formulas/mathematics/high-school/u2zh6atmobu8pylyyhrjk8f41mol6cwppd.png)
We know that the perimeter is 86. Substitute that for P:
![86=2(l+w)](https://img.qammunity.org/2021/formulas/mathematics/college/gelm9r2y6gd119tocjs72yw8b9oq37rbbz.png)
Substitute (x+5) for the length l and 17 for w. So:
![86=2((x+5)+17)](https://img.qammunity.org/2021/formulas/mathematics/college/zraeo6qilqxuv3squj9b6ab93jwpjt4bpn.png)
We can simplify this to acquire our equation:
![86=2(x+22)](https://img.qammunity.org/2021/formulas/mathematics/college/5wzvdm7518h9p7d5fsc8i6wmgupwcjhdzn.png)
Part B)
To find the length, let's find our x first. We have the equation:
![86=2(x+22)](https://img.qammunity.org/2021/formulas/mathematics/college/5wzvdm7518h9p7d5fsc8i6wmgupwcjhdzn.png)
Divide both sides by 2:
![43=x+22](https://img.qammunity.org/2021/formulas/mathematics/college/ydcxkslmxo4e1r0p304enbzgqdz9krnvdn.png)
Now, subtract 22 from both sides. Therefore, our x is:
![x=21](https://img.qammunity.org/2021/formulas/mathematics/middle-school/9xb8efurl8jk1gyvp9186n9hggyidu2tnq.png)
To find the length, remember that the length is:
![l=x+5](https://img.qammunity.org/2021/formulas/mathematics/college/vli22hanigp5r4gcz57uoga21z6cric197.png)
Since we now know the value of x, substitute 21 for x:
![l=21+5](https://img.qammunity.org/2021/formulas/mathematics/college/4xi9tnz240clf1y5npe69e0qvre34614wh.png)
Add:
![l=26\text{ cm}](https://img.qammunity.org/2021/formulas/mathematics/college/qwd6ukyka9rg9ig0o4undsgx5w3kg2jm50.png)
So, the length is 26 centimeters.
And we're done!