[tex]\bf \cfrac{3}{4}x+\cfrac{5}{8}=4x\impliedby \textit{let's multiply both sides by }4\cdot 8=\boxed{32}
\\\\\\
32\cdot \cfrac{3}{4}x+32\cdot \cfrac{5}{8}=32\cdot 4x\implies 24x+20=128x[/tex]
and surely you know how much that is.
to get rid of the denominators, you can simply get their LCD and multiply both sides by it.
