Y-intercept is the y-value when x = 0. Let's consider coordinates (1, 11) and (2, 14). The x-value increased by 1 and the y-value increased by 3. If we assume this is linear, which it is, then the slope is 3. y = 3x + b. We solve b by plugging in a random set of coordinates, such as (1, 11).
11 = 3(1) + b
b = 11 - 3
b = 8
y = 3x + 8 is the equation, slope of 3 and y-intercept is 8.