How do you solve he formulas for numbers 9 and 10?

How do i do this activity, is appreciated

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?

Wrote and expression for the difference of p and 4