1/6 of an hour is equivalent to 10/60 or 10 minutes.
To find out how much 3/4 of an hour is, change the denominator of both fraction so that they match up. We can make this easier by multiplying 4 by 15 to get 60 (hence an hour) and since we multiplied 4 by 15, we also need to multiply 3 by 15 which gets us 45.
We end up with 10/60 and 45/60 or 10 minutes and 45 minutes.
Half of 10 is 5 so we know we'll have a decimal of .5 in our answer.
4 times 10 equals 40 and 40 plus 5 equals 45, so 4.5.