im having a difficult time in trig, and this would be really helpful to understand:)) <3

What is always true when two whole numbers are subtracted?

Becca wants to mix fruit juice and soda to make a punch. she can buy fruit juice for $3 a gallon and soda for $4 a gallon. if she wants to make 28 gallons of punch at a cost of $3.25 a gallon, how many gallons of fruit juice and how many gallons of soda should she buy?

Five infinity stones cost $16.80. what is the price per infinity stone ?