Step 1 :\(\frac{5x}{15} + \frac{3x}{15} = 8\)
Step 2 :\(\frac{5x+3x}{15} = 8\)
Step 3 :\(\frac{8x}{15} = 8\)
Step 4 :\(8x = 120\)
Step 5 :\(x = 15\)
Step 6 :\(\frac{15}{3} + \frac{15}{5} = 8\)
Step 7 :\(5 + 3 = 8\)
Step 8 :\(\boxed{15}\)