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**G-Rex** Could anyone give me a hand with these? I'm stuck on quite a few of them (more to come).

**1)The altitude of a triangle is increasing at a rate of 2 cm/min, while the area of the triangle is increasing at a rate of 2 cm^2/min. At what rate is the base of the triangle changing when the altitude is 10 cm and the area is 80 cm^2?**

The formula I'm coming up with to solve is a'=.5(b')(h) + .5(h')(b). Then, plugging in the values given me, I get 2=.5(b')(10) + .5(2)(16), solving for b by solving a=.5(a)(b), in this case being 80=.5(10)(b). However, when I solve for b', I get -14/5, which is incorrect. What am I doing wrong here?