The area of a rectangle is length times width.
So in this case, 51=(x+5)(3 2/5)
Rewrite the fraction to be improper so 51=(x+5)(17/5)
Now solve...
51=17x/5+17 Now subtract 17 for both sides.
34=17x/5 Now cross multiply to solve for x.
34(5)=17x
170=17x
X=170/17=10
So, the length is x+5=10+5=15 inches
Check: A=(15)(3 2/5) = (15)(17/5) = 51 correct area
ANSWER: length=15 inches