To solve the equation \( 20 = 5 - \frac{3}{8}x \), follow these steps:
- Start by isolating the variable term. Subtract 5 from both sides:
\[ 20 - 5 = -\frac{3}{8}x \]
This simplifies to:
\[ 15 = -\frac{3}{8}x \]
- To eliminate the negative sign and the fraction, multiply both sides by -1:
\[ -15 = \frac{3}{8}x \]
- Now, to solve for \( x \), multiply both sides by the reciprocal of \( \frac{3}{8} \), which is \( \frac{8}{3} \):
\[ x = -15 \times \frac{8}{3} \]
- Calculate the right-hand side:
\[ x = \frac{-15 \times 8}{3} = \frac{-120}{3} = -40 \]
Thus, the solution is:
\[ \boxed{-40} \]
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