Question 251909
This makes no sense. 
"The boat's engines drive in still water at an average rate of 16 mph greater than the rate of the current."
Either the water has a current or not. If there is a current, the water is not still.
r*t=d
(16+r)*t=78
t=78/(16+r)
(16-r)*t=48
t=48/(16-r)
78/(16+r)=48/(16-r)
r = 80/21 
r=~3.80952 current

r=~19.80952 boat with current
r=~12.19048 boat against current