Write the Statement as a Power Function Equation $t$ Varies Inversely as the Speed

Write the statement as a power function equation. Use k as the constant of variation.
-John kept track of the time it took him to drive to college from his home and the speed at which he drove. He found that the time $t$ varies inversely as the speed $r$ .

A) $\mathrm { r } = \mathrm { kt }$
B) $t = \frac { k } { r }$
C) $t = \frac { r } { k }$
D) $t = k r$