Answer
less than $80$ miles
Work Step by Step
Let $x$ be the number of daily miles to drive the compact car.
The conditions of the problem translate to
\begin{array}{l}\require{cancel}
24+0.15x\lt36
.\end{array}
Using the properties of inequality, then
\begin{array}{l}\require{cancel}
0.15x\lt36-24
\\\\
0.15x\lt12
\\\\
x\lt\dfrac{12}{0.15}
\\\\
x\lt80
.\end{array}
Hence, if the daily miles of the car is $\text{
less than $80$ miles
,}$ Plan A is more economical than Plan B.