Well first you must find what 71/2 is equal to:
71 / 2 = 35.5
Now you should convert this to a decimal instead of a percent. All you have to do is move the decimal two places to the left when going from percent to decimal:
35.5% = .355
Now that you know the decimal value, you want to know what number is 12 35.5% of. To do this, think, if you were wondering what is 10% of 100, you would multiply 100 by .10 so in this case since you are going the opposite way, you would divide 12 by .335, which gives you:
35.8208955224
This can be approximated to:
≈35.82