Thank you for the opportunity to help you with your question!
I see your solution step is on the right path. You are almost there in finding the y-intercept. Now that you have y = 3x + b , we have the variables x, y, and b to deal with. But we can substitute for x and y from either of the given points (2, 5) or (4, 11). Let us choose point (2, 5).
x = 2 and y = 5,
From y = 3x + b
so 5 = 3*2 + b,
5 = 6 + b,
therefore b = -1
Your y-intercept is -1
Please let me know if you need any clarification. I'm always happy to answer your questions.
Nov 7th, 2015
But to completely answer question #31.) we say the linear equation is y = 3x - 1 which contains the points (2, 5) and (4, 11).