We start with the equation: \[ 3x + 5 = 20. \] To isolate \( x \), first subtract 5 from both sides: \[ 3x = 20 - 5 \implies 3x = 15. \] Now, divide both sides by 3 to solve for \( x \): \[ x = \frac{15}{3} = 5. \] Thus, the correct answer is (B) 5.