You can set up a proportion: 1/2:1/15=x:1

Cross multiply:
1/2=1/15x

Divide both sides by 1/15:
7.5=x

Robert can run 7.5 miles in an hour

15/30:2/30

15/30=2/30x

divide by 15/30

7.5 is x

Step-by-step explanation:

to rewrite a literal equation you may need to divide by a number, or by a variable.

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$54.99

step-by-step explanation:

$54.99 includes 500 min. if she does not exceed 500 min then her bill is $54.99