Divide 45 by 10 and once you do that you should see that the answer is 4 with a remainder of 5. The remainder will go on top of a fraction (as the numerator) and 10 will remain as the denominator. The number 4 will be the whole number.
So 45/10 as a mixed number is 4 5/10. But 5/10 can be reduced to 1/2 (if you divide the numerator and the denominator by 2). The simplified answer would be 4 1/2.