Rafe burns 4.5 calories in 2/3 of a minute riding his bike. what is rafe's unit rate?

What I believe you have to answer is how many calories Rafe burns per minute. 
If in 2/3 of a minute he burns 4.5
1/2 of 4.5 I believe would be 1/3 of x.
x being the total calories he burns in a minute.
So, 1/2 of 4.5 is 2.25.
1/3 of x is 2.25
2/3 of x is 4.5
2.25+4.5=6.3
Rafe burns 6.3 calories per minute.
Hope this helps :)