Convert the second point from "hours" to "minutes", so you have the same units.
Then use the fact that they've given you two points in the form (x, y) = (minutes, cost), along with the formula for slope to find the slope of the line through these two points.
Then take one of the points (it doesn't matter which) and the slope you just found, and plug them into one of the straight-line formulas, such as the point-slope formula, to find the equation of the straight line through these two points.
If you get stuck, please reply showing how far you have gotten. Thank you!