So confused on this?

Which of the following is a function? a.) {(-2, -4/5), (-1,-,,-1)} b.) {(-2,,1/,3/,1)} c.) {(-22)} d.) {(-21)}

Erin bought christmas cards for $2 each to send to her family and friends. which variable is the dependent variable?

10 points? me . its important ‼️‼️