If she wants to make 12 servings for every 5 people, for 10 people she would need 24 servings. If each pan hold 8 servings you would divide 24 by 8 which gives you 3 therefore she would need to order 3 pans.
The expression –3 + 2x is equivalent to 2x – 3. I know it is equivalent because for every value of x that is substituted in, the two expressions simplify to the same value. I took the expression and used the commutative property to not change the value.