I can deduce from here that you are trying to find "a", and "/" stands for divide
2/a = (5/2) / (5/4)
2/a = (5/2) x (4/5) this is called the inverse multiplication where the division sign changes to a multiplication sign and the fraction is turned upside down.
2/a = (20/10)
2/a = (2)
since you are trying to solve for "a", you can either cross multiply then you have
2 = 2a, then divide both sides by 2 and your answer becomes a = 1 or you multiply both sides by "a" then you have (2 = 2a), divide both sides by a and your answer becomes a = 1
I hope this really helps you
xoxoxo