Answer:
y = m x + b standard equation of straight line
When x = 0 y = -1/2 from graph
y = m x - 1/2 equation becomes
Now when x = 2, y = 3.5 given
m = (y + 1/2) / x
m = (3.5 + .5) / 2 = 2 from given value
y = 2 x - 1/2 final value for straight line
Check: use x = 1 and y = 1.5
y = 2 * 1 - 1/2 = 1.5 calculated value agrees with given value