Answer:
the solution for the system is;

Step-by-step explanation:
Let C be the number of cheetos bags that you will buy and T the corresponding number of Takis bags.
Since you're going to buy a total of 30 bags, then;

Since the Cheetos bag cost $15, then the total cost for C bags is 15C. The same way, since the Takis bag cost $40, the total cost for T bags is 40T. Since you will spend $750, then;

Use the substitution method to solve the system. To do so, isolate one variable from the first equation and substitute the resulting expression into the second equation;

Substitute that expression for C into the second equation and solve for T:

Substitute back T=12 into the expression for C;

Therefore, the solution for the system is;

Which mean that you buy 12 bags of Takis and 18 bags of Cheetos.