Variable $x$ cannot be equal to $0$ since division by zero is not defined. Multiply both sides of the equation by $15x$, the least common multiple of $x,3x,5x,15$.
$$15\times 3-5\times 8+3\times 4=x$$
Do the multiplications.
$$45-40+12=x$$
Subtract $40$ from $45$ to get $5$.
$$5+12=x$$
Add $5$ and $12$ to get $17$.
$$17=x$$
Swap sides so that all variable terms are on the left hand side.
