Explanation

Given that x = 3 is a solution to the equation:

x² + rx - 20 = 4

Substitute x = 3 into the equation:

(3)² + r(3) - 20 = 4

Simplify:

9 + 3r - 20 = 4

Combine like terms:

3r - 11 = 4

Add 11 to both sides:

3r = 15

Divide by 3:

r = 5