Find the sum of the prime numbers less than 21

In the surface area formula for cylinders which expressionrepresents the lateral area

Abby is preparing fruit punch for her party. she starts with a bowl filled with liquid that has 1/2 fruit juice and 1/2 sprite, but she decides it's too fruity. so she pours out 1/4 of the liquid, and then fills the bowl up again with sprite. what fraction of the punch is now sprite?

What is the value of m in the equation 1/2 m - 3/4n=16 when n=8