Simplify the given expression: 10. $\frac{1}{3}(12 x-21)-\frac{3}{4}(4 x-20)$

Step 1 ：Distribute the fractions in each term over the binomial: \(\frac{1}{3}(12x-21)\) becomes \(4x-7\) and \(\frac{3}{4}(4x-20)\) becomes \(3x-15\).

Step 2 ：Subtract the second term from the first term: \((4x-7)-(3x-15)\).

Step 3 ：Simplify the expression by combining like terms: \(4x-3x\) becomes \(x\) and \(-7-(-15)\) becomes \(8\).

Step 4 ：So, the simplified form of the given expression is \(\boxed{x + 8}\).