Elimination or subtraction method to find the solution of Y=10x+24 and y=15x-75

How can you decide witch operations to use to slice a two step equation

Parks is wearing several rubber bracelets one third of the bracelets are tie-dye 1/6 are blue and 1/3 of the remainder are camouflage if parks wears 2 camouflage bracelets how many bracelets does he have on

This is about circle theorems. someone asap : (