Let the sandbox width = W and the length L = W+4

The condition for the grass and the sandbox is modeled by (W+10)(W+4+10) = 190 or

(W+10)(W+14) = 190 = W2 + 24W + 140 or w2 + 24W -50 = 0

The roots are W = -25.93 and 1.93 So the real answer for W = 1.93, Therefore, L = W+4 = 5.93