So in total, you're going to need 75 pencils and 45 erasers.
If pencils cost 10 cents, you multiply 75 by 10 and get 750 cents or $7.50.
If erasers cost 5 cents, you multiply 45 by 5 and get 225 cents or $2.25.
When you add them together, you get $9.75 in total.
SC spent $9.75 in all.