ANSWER
12 runs
Step-by-step explanation
We have that the baseball pitcher allowed 3 runs in 9 innings.
Let the number of runs he allowed in 36 innings be x.
This means that:
3 runs = 9 innings
x runs = 36 innings
Cross-multiply:
=> 3 * 36 = 9 * x
Divide both sides by 9:
Therefore, at this rate he would allow 12 runs