First set everything to 0.

Giving you A= 1 , B= 1 and C= -5
Then input everything into the quadratic formula and either solve by hand or use a calculator.
Note exact values are found by hand, decimals are found using a calculator.
Step-by-step explanation:
RS = RT-ST
................
It is a decimal that does not go in forever.
The number of ways of picking up a red cube out of 12 cubes are 5/12. Number of ways of picking up a second red cube is 4/11.
<span>Thus probability of picking up 2 red cubes = 5/12 * 4/11 = 20/121.
20 / 121 = .165 or .17
So the probability of Celinda getting two red cubes is .17.</span>