numerator/denominator
First we need to find the common denominator (a number that can be divided by both 3 and 4)
3 x 4 = 12 (so our new, common, denominator is 12)
Whatever we do to the bottom of a fraction (the denominator) we must also do to the top
For 2/3 we multiplied 3 (the denominator) x 4 to get the new common denominator (12) and so we also need to multiply the numerator (2) by 4
2/3 = 8/12
For 1/4 we multiplied 4 (the denominator) x 3 to get the new common denominator (12) and so we also need to multiply the numerator (1) by 3
1/4 = 3/12
So our new problem is 8/12 - 3/12
Working across the numerators we do our subtraction problem, but the denominator will remain the same
8/12 - 3/12 = 5/12 (this is the final answer as this fraction cannot be simplified any further)