What effect does "a" have on a fuction f(x)=a(x-h)^2+k

Aquantity with an initial value of 3900 decays exponentially at a rate of 35% every hour. what is the value of the quantity after 0.5 days, to the nearest hundredth?

Given a: b and b: c, find a: b: c. write the ratio in simplest form. a: b=6: 10 and b: c=21: 33

Write the point-slope form of the line passing through (2, -12) and parallel to y=3x.