Variable $x$ cannot be equal to $0$ since division by zero is not defined. Multiply both sides of the equation by $28x$, the least common multiple of $4x,7x,28$.
$$7\times 3-4\times 2=x$$
Do the multiplications.
$$21-8=x$$
Subtract $8$ from $21$ to get $13$.
$$13=x$$
Swap sides so that all variable terms are on the left hand side.
