3,150 doesn't need to be simplified. so, i guess if it were to be simplified, it would just stay the same.
we are given
The water level in Ricky lake changes at an average of -7/48 inch for 1 year
It means that
In 1 year , the water level changes at 
and we have to find the water level change after 5 years
so, we can multiply both sides by 5
In 5*1 year , the water level changes at 
In 5 years , the water level changes at 
Hence,
the water level change after 5 years is
........Answer
Because completementary angles add up to 180 degrees (angle 3 and angle 4)
and interior angles of a triangle will also add up to 180 degrees
if you compare these two facts, then angle 4 equals the 2 non adjacent interior angles