Substitute to Find the Value of the Expression $\frac{2520}{t}$ Where $t$ Is the Time, in Hours, to Complete the Trip

Substitute to find the value of the expression.
-A train must cover a distance of 2520 miles. The velocity, in miles per hour, of the train is $\frac{2520}{t}$ where $t$ is the time, in hours, to complete the trip. If the train completes the trip in 28 hours, what is its velocity?

A) $70,560 \mathrm{mph}$
B) $0.01 \mathrm{mph}$
C) $90 \mathrm{mph}$
D) $85 \mathrm{mph}$