The domain of the equation are all the possible values of the independent variables that would make the equation reasonable, possible or true. In this item, the independent variable is r. This could take a value of 0 up to the point when m is equal to zero.
m = 30 - 3r = 0
r = 10
The domain is therefore [0, 10].
The range is the value of the dependent variable which would be from 0 to the point when no video game is played. This is, [0, 30].
The function is discrete because r and m cannot take every value in the number line.
When you divide two fractions, you're actually multiplying one of them by the reciprocal of the other. First, find the reciprocal of the second fraction by flipping it upside down. Then, multiply it by the first fraction. (Numerator x numerator and denominator x denominator)
÷
Replace the second fraction with it's reciprocal
x
Multiply (-7 x 3 and 12 x 2)
Both 21 and 24 are divisible by three, so divide them by 3
If you do the long division you'll see that it is x - 2.