To find the combined area of the garden and the walk, we need to find the dimensions of the largest rectangle that contains them.
To get this, we need to add the width of the walk to the dimensions of the garden.
The new dimensions would be
35 + 2(x+2) ft by 25 + 2(x+2) ft
Note that we need to add twice the width of the walk since it is around the garden. (top and bottom, left and right)
Therefore, the expression for their combined area is
A = [35 + 2(x+2)] • [25 + 2(x+2)] = (2x+39)(2x+29) = 4x² + 136x +1,131