Which graph shows h(x) = (f(x)) + (g(x))?

7.5 mph.

Step-by-step explanation:

Speed downstream = d / 3 = 30 + x    where d = the distance , x =speed of the stream.

Speed upstream = d  / 5 = 30 - x.

30 + x = d/3

30 - x = d/5

Adding the 2 equations

60 = d/3 + d/5

8/15 d = 60

d = 60 * 15 / 8 =  112.5 miles.

Now calculate x , the speed of the stream:

112.5 / 3 = 30 + x

x = 112.5 / 3 - 30

= 7.5 mph.