Your method is right so u already know how to do it
Part A:
Let the width of the rectangle be = x inches
As given, the length of a rectangle is 3 more inches than the width so let the length of the rectangle be = x+3 inches
Perimeter is given as = 54 inches
Perimeter = 
Equation becomes:
=54

Part B:
Solving the equation we get




Hence, the width of the rectangle is 12 inches
Length = x+3 = 12+3 = 15 inches
Hence, length of the rectangle is 15 inches.
X^-6
You can find the derivative:
-6x^ -7
The answer is 90x2y3 since 18 and 15 have an LCM of 90, and x2y3 and xy2 have an LCM of x2y3.