Chapter 1 - Section 1.7 - Problem Solving: Interest, Mixture, Uniform Motion, Constant Rate Job Applications - 1.7 Asses Your Understanding - Page 141: 27

$2.285$ miles an hour.

Let $x$ be the current velocity, then the upstream velocity is $16-x$, the downstream velocity is $16+x$. Then our equation is: $(16-x)\cdot20=(16+x)\cdot15\\320-20x=240+15x\\80=35x\\x\approx2.285$ Thus the current speed is $2.285$ miles an hour.