For the first one, cross multiply 15 and c which is 15c and cross multiply 8 and 45 which is 360, so u get 15c = 360 and divide 15 c by 15 and 360 by 15 also then the answer would be c = 24
For the second one it’s basically the same thing, cross multiply x and 12 which is 12x and 8 and 3 which is 24, then you get 12x = 24. Divide both sides by 12 and the answer would be x = 2