In the table for C, put the y into the equation, for example, 7. The equation becomes 7 = 3x + 4. Plug in the x variable, which in the case of 7 is 1. Now the equation is 7 = 3(1) + 4. 3 times 1 is 3. Now it is 7 = 3 +4. This is true, and that is why the answer is C.