Answer:
x = 6 cm
Explanation:
The area is the product of length (x +2) and width (2x -5). It is 56 cm², so for all dimensions in cm, we can write ...
(x +2)(2x -5) = 56
2x² -x -66 = 0 . . . . . subtract 56 to put into standard form
(x -6)(2x +11) = 0 . . . . factor
Solutions to the equation are values of x that make the factors zero:
x = 6, x = -11/2
The negative solution is extraneous, so the solution of interest is ...
x = 6 cm