Can someone me understand how to do this equation?

System A --> B

Equation A1 and B1 the same, but B2 changes. The change is that the whole equation is multiplied by 4. So, the answer is B and 4 goes in the blank

System B --> C

Equation B1 and C1 are the same, but C2 changes. This change is not multiplication, so our only option now is C. In C2, the x-factor is removed, which means that elimination occurred. -12/-3 = 4, so in the blank, 4 goes in.

the correct answer is 5