: 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.
First off, you need to isolate t so that you can find its answer.
If you have R = -0.037t + 50.1, here are the following steps to isolate.
R - 50.1 = -0.037t (switch the 50.1 on the other side)
( R-50.1 ) / -0.037 = t
you can replace R by the time, in your case 48.1.
( 48.1 - 50.1) / -0.037 = t
(-2) / -0.037 = t
t = 54.054
Therefore, after 54.054 (or 55 if you round up) years after 1925 the 400 meter dash will be under 48.1 sec.
You can also add the year ( 1925 + 55 = 1980) in your final answer