What is the equation of a line that passes through the points (3, 6) and (8, 4)

First let us find the slope between the two points.

Slope = Change in y / Change in x.

(3, 6) and (8, 4) compares to (x₁, y₁) and (x₂, y₂)

Slope = (y₂ - y₁) / (x₂ - x₁) =  (4 - 6) / (8 - 3) = -2/5 

Slope m = -2/5= -0.4

Using  y = mx + c,   using point (3, 6)

y = -0.4x  + c

6 = -0.4*3 + c

6 = -1.2 + c

6 + 1.2 = c

7.2 = c

c = 7.2

Equation = :       y = -0.4x +c

y = -0.4x + 7.2

y = -4/10  + 72/10

10y = -4x + 72

5y = -2x + 36

Equation =:      5y = -2x + 36

Hope this explains it.