posted by Sara .
If the formula R= -0.0371 + 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 record be 48.1 secons or less?
There is no t in your formula. You copied it wrong.
When you have the right formula, set it equal to 48.1 and solve for t. Add that to 1925. Later years will have a lower record, supposedly.
Of course, world records do not change at such a smooth rate. It is an approximation.