If you inspect the y values, you will note that the y value goes up one for every value of x.
If you are already using slope, that means that the slope is 1. With slope-intercept form, you need to know two things: the slope and the y value where x = 0. Here y = 7 where x = 0.
So the formula for the line is y = x + 7.
Question B asks what is the value of y when x = 8. Just substitute x with x in the equation above and you get: y = 8 + 7. That simplifies down to y = 15.
Question C asks what is the value of x when y = 35. So to do that, we substitute y with 35:
35 = x + 7
35 - 7 = x + 7 - 7
28 = x
So when y = 35, x = 28. And there you have it!