15,3-3·(6¾-3,35)

To solve the expression \( 15.3 - 3 \cdot (6\frac{3}{4} - 3.35) \), we will follow the order of operations (parentheses, exponents, multiplication and division from left to right, addition and subtraction from left to right).

1. Convert \( 6\frac{3}{4} \) to an improper fraction: \[ 6\frac{3}{4} = 6 + \frac{3}{4} = \frac{24}{4} + \frac{3}{4} = \frac{27}{4} \] In decimal form, \( 6\frac{3}{4} = 6.75 \).

2. Calculate the expression inside the parentheses: \[ 6.75 - 3.35 = 3.40 \]

3. Multiply by 3: \[ 3 \cdot 3.40 = 10.20 \]

4. Subtract from 15.3: \[ 15.3 - 10.20 = 5.10 \]

The final answer is: \[ \boxed{5.1} \]