Find the probability of Red/small.
Red = large + small
large = 8
Small = 12
Plug in 8 for large, and 12 for small
Red = 8 + 12
Red = 20
Now we know that the total red = 20
Do the same with small
3 small blue
12 small red
Small = blue + red
Small = 3 + 12
Small = 15
Note that red is first then small. Put red over small
Remember that red = 20, small = 15
20/15 is the fraction you need.
However, note that it says "reduce your answer" at the bottom
Divide 5 from numerator and denominator
(20/15)/(5/5) = 4/3
4/3 is your answer
hope this helps