Evaluate the expression when \( x=\frac{3}{10} \) and \( y=-\frac{3}{20} \). \[ 4 y-x \] Write your answer in simplest form.

To evaluate the expression \( 4y - x \) when \( x = \frac{3}{10} \) and \( y = -\frac{3}{20} \), we start by substituting the values of \( x \) and \( y \). First, we calculate \( 4y \): \[ 4y = 4 \left(-\frac{3}{20}\right) = -\frac{12}{20} = -\frac{3}{5} \] Next, we substitute \( 4y \) and \( x \) into the expression: \[ 4y - x = -\frac{3}{5} - \frac{3}{10} \] To perform this subtraction, we need a common denominator. The least common denominator between 5 and 10 is 10. We convert \(-\frac{3}{5}\) to the same denominator: \[ -\frac{3}{5} = -\frac{6}{10} \] Now, we can substitute this back into the expression: \[ -\frac{6}{10} - \frac{3}{10} = -\frac{6 + 3}{10} = -\frac{9}{10} \] Thus, the value of the expression \( 4y - x \) when \( x = \frac{3}{10} \) and \( y = -\frac{3}{20} \) is: \[ \boxed{-\frac{9}{10}} \]