This question is asking us the unit rate, so we need to make a proportion.
[tex] \frac{4.5}{2/3} = \frac{x}{1 minute} [/tex]
When we solve it, we end up with:
4.5 = 2/3x
And now you substitute:
[tex] \frac{4.5}{2/3} = \frac{2/3x}{2/3} [/tex]
And you end up with your answer:
Blake burns 3/4 calories per minute.
