Answer:
<em>The speed of the current is </em><em>4 miles/hour</em>
Step-by-step explanation:
Let us assume that,
x = speed of the boat,
y = speed of the current.
We know that,

A motorboat can go 8 miles <em>downstream</em> on a river in 20 minutes or
hours.

--------------------------1
It takes 30 minutes for the boat to go <em>upstream</em> the same 8 miles.

----------------------------2
Subtracting equation 1 and 2,


miles/hour