I need help solving this please

Name the most appropriate metric unit for each measurement

Evaluate the expression for the given value of the variable 2×(c2-5) for c=4

Galen sold tickets of his church’s carnival for a total of $2,820. children’s tickets cost $3 each and adult tickets cost $5 each. the number of children’s tickets sold was 30 more than 3 times the number of adult tickets slod. how many children’s ticket and how many adult tickets did he sell?