Answer:
= 18 red marbles
Explanation:
Let x be the number of red marbles that must be added
Therefore;
New number or red marbles = x+12
Total marbles will be x+32
Thus;
The probability of selecting a red marble = (x+12)/(x+32)
Therefore;
(x+12)/(x+32)=3/5
5(x+12)=3(x+32)
5x+60+3x+96
2x=36
x=18