Let

v = 16 mph the speed of the boat in still water

c = the current of the stream

d = 58 miles the distance traveled in one direction

t = the time of the travel downstream

t + 1 = the time of the travel upstream

the speed upstream is: v - c

the speed downstream is: v + c

Since speed = distance/time => time*speed = distance

t(v + c) = d

t(16 + c) = 58

t = 58/(16 + c)

(t + 1)(v - c) = d

(t + 1)(16 - c) = 58

lets plug t = 58/(16 + c) into the last equation

(58/(16+ c) + 1)(16 - c) = 58

........

........

c = 2.17 mph

The rate of the current is 2.17 mph.