x = plan A
y = plan B
9x + 7y = 12
3x + 5y = 6
**Find an equation for x**
3x = 6 - 5y
x = 2 - 5/3y
**Use substitution**
9( 2 - 5/3y) + 7y = 12
18 - 45/3y + 7y = 12
18 - 15y + 7y = 12
-8y = -6
y = 3/4
x = 3/4
Each of the workouts last 3/4 of an hour, or 45 minutes.