First you have to find the slope(m). To find the slope you take two points[(2,5) and (8,9)] and make it so (9-5)/(8-2) which is a slope of 2/3.
Substitute that in for m.[y=2/3x+b]
Next Substitute one of the two points into the equation. [5=(2/3)(2)+b]
Solve for b. [5-(4/3)=b]
Simplify. [11/3=b]