For a continuous function f, the sign of f on several intervals is given below:
• f(x)<0 on (−3,0)
• f(x)>0 on (0,4)
• f(x)<0 on (4,6)
Let g(x)=∫−3xf(t)dt. On which of the following intervals must g be increasing?
a) (−3,0)
b) (−3,4)
c) (0,4)
d) (0,6)