Answer:
20 minutes on the stationary bike
10 minutes on the treadmill
Step-by-step explanation:
x = minutes on bike
y = minutes on treadmill
x + y = 30
12x + 15y = 390
x = 30-y
12(30-y) + 15y = 390
360 - 12y + 15y = 390
3y = 30
y = 10
x + 10 = 30
x = 20
