1) In order to solve a system of equations with the elimination method, you need to add or subtract the two equations and "eliminate" variables by canceling out terms. This leaves you with an equation with only one variable to solve. Then, once you solve that equation, you can substitute the answer you got into one of the system's equations to find either the x or y value.

This problem already has one 3x in each equation, so let's focus on canceling that term out, eliminating the x variable. To set up this situation, we need one 3x to be negative, so let's multiply the terms in 3x-6y = 4 by -1, which gets us to -3x + 6y = -4. Now let's "cancel out" those x variables by adding them together. (This work is shown in the first picture.)

Remember to add the other terms. This leaves us with the equation 13y = 13. By isolating y, we can find its value, which leaves us with y = 1.

2) Next, let's substitute 1 for y in one of the two equations. In this case, I used 3x + 7y = 17. Then, isolate x to find its value:

$3x + 7 (1) = 17\\3x + 7 = 17 \\3x = 10 \\x = \frac{10}{3}$