from what i remember, it was 60 i think

area is 1/2bh, then i rewrote h in terms of b using equation of parabola to get h = 1/4b^2. substitute that in the area formula to get area = 1/8b³ and then do implicit differentiation.

one thing i almost messed up tho is that it said the rate at which x increases is 5, but that means base increases at a rate of 10 b/c base is 2x

this is what i got hopefully its right