Chapter 2 Linear Equations and Functions - 2.5 Model Direct Variations - 2.5 Exercises - Problem Solving - Page 110: 38

See below.

If the variables vary directly, then $d=at$ for some constant $a$. Plugging in the given values, here $45=a\cdot0.75\\a=60$. Thus the equation is: $d=60t$. Thus if $d=100$, then $100=60t\\t=\frac{100}{60}=\frac{5}{3}$