How do you know that ADB and BDC are supplementary?

An architect is designing a water fountain for a park she uses the given function to model the water jet flowing from the fountain nozzles where h(x) gives the height of the water jugs in feet x feet from the starting point h(x)=-1/20x+x+15

Present age of man is 45 years, 5 years back his age was 4 times age of his son what is present age of his son?

3.4a=57.8 what is the the value of a