83.33 meter per minute

.

His rowing speed is 83.33 m/min

The stream speed is 16.67 m/min.

.

That means his speed on the first trip is 66.67 m/min => 1500 m in 22.5 min = 1350 sec

And the trip back his speed is 100 m/min => 1500 m in 15 min.

.

-7.5x+37.5y = 3000

-22.5x+22.5y = 1500

-45x+45y=3000

.

(45-37.5)y=(45-7.5)x

7.5y=37.5x

y=5x

3000=(37.5*5-7.5)x

x = 16.67