At 10 hours they'll both have $84 to go to the movies.
Step-by-step explanation:
Mai:
7h+14=x
1 hour : 21; 2: 28; 3: 35; 4: 42; 5: 49; 6: 56; 7: 63; 8: 70; 9: 77; 10: 84
Priya:
8.4h=x
1 hour: 8.4; 2: 16.8; 3: 25.2; 4: 33.6; 5: 42; 6: 50.4; 7: 58.8; 8: 67.2; 9: 75.6; 10: 84