If a* b= 0 then what do we know about a and or b

Aculture started with 3000 bacteria. after 5 hours it grew to 3900 bacteria. predict how many bacteria will be present after 9 hours

If f(x) = x+8 and g(x) = 4x- 3, find (f+g)(x)

What is the volume of a rectangular crate that has dimensions 9 inches by 9 inches by 1 feet? 1,458 in.3 121.5 in.3 1,012.5 in.3 36 in.3