If the formula R = -0.037t + 50.1 can be used to predict the world record in the 400-meter dash t years after 1925, for what years will the world records be 48.1 seconds or less?
Do I replace t with 48.1 seconds and solve for R?
Strictly speaking, no, it is not right. The problem asked "for what years will the world records be 48.1 seconds or less" and you have not yet answered that question. What you have said is that the record should be down to 48.1 seconds or less 54.1 years after 1925. What years will those be?
(And was it?)