To solve this problem you would break it down .. step by step
1300/x = 100/8
{1300/x) *x = (100/8) ^x - multiplying both sides of equation by the x
1300 = 12.5*x { 100/8 gets 12.5}
1300/12.5 = x
and last .. but not least divide 1300/12.5 and you get ..
x = 104 >> 8% of 1300 = 104 or 1300 of 8% = 104