Question 165404
You are given:
R = -0.037t + 50.1 
where
R is the record
t is years after 1925
.
So, they want to know when the record will be 47.6 seconds or less...
So, just "plug it in" and solve for 't':
R = -0.037t + 50.1 
47.6 = -0.037t + 50.1 
47.6 + 0.037t = 50.1 
0.037t = 2.5
t = 2.5/0.037
t = 67.568 years after 1925
.
So, 
1925 + 67.568 = 1992.568
.
Conclusion:
1992 and AFTER the world record will be 47.6 seconds or less