Answer:
15 hard problems
Step-by-step explanation:
set x = easy problems, y = hard
x + y = 50
30x + 60y = 1950
x = 50-y
30(50-y) + 60y = 1950
1500-30y + 60y =1950
1500 + 30y = 1950
30y = 450
y = 15
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