Chapter 2 Linear Equations and Functions - 2.5 Model Direct Variations - 2.5 Exercises - Problem Solving - Page 110: 41

$t=5.1s$

If the variables vary directly, then $t=as$ for some constant $a$. $\frac{23}{4.5}\approx5.1$ $\frac{40}{7.8}\approx5.1$ $\frac{82}{16}\approx5.1$ Thus there is a direct variation with $a=5.1$, and the equation is: $t=5.1s$