Chapter 1 - Section 1.7 - Problem Solving: Interest, Mixture, Uniform Motion, Constant Rate Job Applications - 1.7 Asses Your Understanding - Page 143: 54

See below.

Let $v$ be the speed of the slower cyclist, then $v+5$ is the speed of the faster one, then our equation is: $(v(v+5))\cdot6=246\\(2v+5)6=246\\12v+30=246\\12v=216\\v=18$ So they are riding at the speed of $18$ and $23$ miles an hour.