Answer:
[tex]22.5\:\text{minutes}[/tex]
Step-by-step explanation:
In 15 minutes, Jennifer has mowed [tex]\frac{2}{3}[/tex] of the lawn (given in problem). This means that it will take her [tex]\frac{3}{2}\cdot 15=22.5\:\text{minutes}[/tex] to mow the entire lawn, assuming a constant rate.
Equation:
Let [tex]x[/tex] represent the entire lawn:
[tex]\frac{2}{3}x=15,\\x=\frac{15}{\frac{2}{3}}=15\cdot \frac{3}{2}=\boxed{22.5}[/tex]