# Precalc

posted by
**Rose**
.

Can someone please help me? I don't know how to solve for time under 23 units. When I try I think I get the answer for above 23 units and when I try to subtract from the whole period my answer is wrong. The correct answer is 5.1337 hours.

Fidel is measuring the light intensity of a distant star. He has found that the intensity varies between a minimum of 19 units and a maximum of 75 units. At 7:00 AM today, he found the intensity was 19. The intensity then increased, reaching an intensity of 47 at 11:00 AM today.

Assume that the light intensity is a sinusoidal function of time. For what length of time today will the intensity be below 23 units?