To find a proper equation in slope-intercept form of the trend line, we can use the points (0, 20) and (40, 78).
Step 1: Calculate the slope using the formula:
m = (y2 - y1) / (x2 - x1)
m = (78 - 20) / (40 - 0)
m = 58 / 40
m = 29 / 20
Step 2: Use the slope and one of the points to find the y-intercept (b). Let's use the point (0, 20).
20 = (29/20)(0) + b
20 = 0 + b
b = 20
Therefore, the equation in slope-intercept form of the trend line is:
y = (29/20)x + 20
y = 1.45x + 20