Now consider the point (0,5) which is part of graph because the gave that the Y intercept is 5 which means the graph intersects the Y-axis at (0,5).
Now, substitute (0,5) in given equation of the graph. Which is,
2(0) + B(5) = 15
5B = 15
B = 3
Hope it helps, feel free to ask doubts if any.
