I’m not sure abt 21 but 22 is the second one and the 4th one. So 2,4.
You multiply both of the equations until you have two of the same term the same like for example, say I have 4x and 5x. You want to multiply until both have the same number, so multiply 5x by four, then multiply 4x by five, and you will get 20x, then both of those cancel out and you will be left with the other variable, and you just solve like a normal equation.
Answer:
the cost of the four meal is $4.00
