Bartolo is running a race. He determines that if he runs at an average speed of 15 feet/second, he can finish the race in 6 seconds. If he runs at an average speed of 18 feet/second, he can finish the race in 5 seconds. What is the constant of proportionality in this indirect variation?

A. 108
B. 75
C. 90
D. 96

This is a rational expression because the denominator contains a variable. this is a polynomial with 3 terms. this is a rational expression because the denominator contains a variable. this is a polynomial with 4 terms. this is a rational expression because the denominator contains a variable. this is a polynomial with 4 terms. this is a rational expression because the denominator contains a variable. this is a polynomial with 3 terms. this is a rational expression because the denominator contains a variable. this is a polynomial with 5 terms.