Answer:
17 cm
Step-by-step explanation:
Area = 1/2(base)(height)
the base is seven less than twice the height, so
b = 2h-7
try to substitute for one of the variables, because it is much easier to solve for them.
b = 2h-7
b+7 = 2h
(b+7)/2 = h
Area = 102
102 = 1/2(b)(b+7)/2
408 = (b)(b+7)
408 = b^2+7b
b^2+7b-408=0
(b+24)(b-17)=0
b = -24 or b = 17
since length can't be a negative number, the length of the base is 17 cm
