Help, being timed!
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11.25

step-by-step explanation:

juan's ratio of violin to cello is

3/2.5

he practices the violin for 9 hours; this gives us the ratio

9/x

for his cello practice.

together we have the proportion

3/2.5 = 9/x

cross multiplying, 3(x) = 9(2.5)

3x = 22.5

divide both sides by 3:

3x/3 = 22.5/3

x = 7.5

juan practices his cello for 7.5 hours.

nina's ratio of viola to cello is

3/2

since she practiced the cello for the same amount of time as juan, that means she practices 7.5 hours.   this gives us the ratio

x/7.5

and the proportion

3/2 = x/7.5

cross multiplying,

3(7.5) = 2(x)

22.5 = 2x

dividing both sides by 2,

22.5/2 = 2x/2

11.25 = x