An algebra problem by Leonardo Vivodra

It might be easier to rewrite question in a little bit "mathematical" form:

$s_1(x)=15x$

$s_2(x)=15x + 2x = 17x$

Question tells us that $x$ is equal to $8$ , so:

$s_1(8)=15(8)=120$

$s_2(8)=17(8)=136$

The question asks how many miles more the second runner would run, so:

$s_2(8)-s_1(8)=136-120=\boxed{16}$