make all of the fractions have the same denominator, although what you do to the bottom you have to do to the top
for example 1:
3/5 - 1/7 the closest denominator that they both are able to multiply up to is 35 (7x5 and 5x7) so change them both and then multiply the top (1x5 and 3x7) then subtract giving you your answer
(not 100% sure i have not done these for years but that’s all i remember if you have notes check those fs!!!!)
