Question 306868
(6, 10.2), (1.5, 3.45), (x, 2.85)

The slope-intercept form of a line is:

y = m*x + b where m is the slope and b is the value of y where the line crosses the x-axis (that is when x = 0 ).

m = (10.2 - 3.45)/(6 - 1.5)
m = 6.75/4.5 = 1.5

We have then 

1.) y = 1.5*x + b. 

Since the line passes through the point (6,10.2) when x = 6, y = 10.2. Substituting these values in 1.) we have: 

10.2 = 1.5*6 + b

10.2 = 9 + b
b = 1.2

The equation of the line is then 

2.) y = 1.5*x + 1.2

To find x for the third point on the line we substitute 2.85 for y in 2.):

2.85 = 1.5*x + 1.2
1.5*x = 2.85 - 1.2
1.5*x = 1.65
x = 1.65/1.5 = ?