I got 12.654 I'm not sure it is right though.
A/4=11/2 if you take 4/2 it equals 2 so you times the numerator and the denomerator by 2 and 11*2 equals 22 so the answer is a=22
It says that there was an error with my answer, but I don't know what, so I screenshotted what I typed and attached them as 4 images below:
defective : working = 1/15 ( x20 ) 20/300
so the answer is 20 light bulbs