7r - 15 / 8, when R = 3 and S = 5
= 7(3) - 15 / 8
= 21 - 15 / 8
= 6/8
= (Now, we will simplify 6/8 and find the least common multiple of 6 and 8 which is 2 so, we will divide 6 by 2 and 8 by 2 and then, that will be our complete simplified fraction!
= (6 divided by 2)/(8 divided by 2)
= 3/4
So, in conclusion, the answer to this equation: 7r - 15/8, when R = 3 and S = 5 is 3/4.