Laugh out loud a pun isn't it
For this case we have the following equation:

We must clear the value of the variable "x" as a function of r, s and t:
If we multiply by "r" on both sides of the equation we have:

If we subtract "t" on both sides of the equation we have:

If we divide by "2" on both sides of the equation we have:

Thus, the value of the variable "x" is:

Answer:

I guess you want the missing angle.
The missing angle is 83
She will need 12 cups of pineapple juice.
Example: 4 x 4 = 16
3 x 4 = 12