The amount Troy charges to mow a lawn is proportional to the time it takes him to mow the lawn. Troy charges $30 to mow a lawn that took him 1.5 hours to mow. Which equation models the amount in dollars, d, Troy charges when it takes him h hours to mow a lawn? A. d = 20h B. h = 20d C. d = 45h D. h = 45d