Given points are .

First, find the slope.

Substitute 20.5 for y₂,  7 for y₁, 1 for x₂, and 3.5 for x₁  in slope formula.

                         (Subtract: )

                              (Subtract: )

                                   (Divide: )

You know the slope and a point on the line, so use point - slope form

with either given point to write an equation of line.

Choose .

                (Substitute 7 for y₁, 3.5 for x₁ and )

          (Apply distributive property: )

                 (Multiply: )

Apply addition property of equality: If a = b then a + c = b + c.

      (Add 7 to each side)

           (Apply additive inverse property: )

                 (Apply additive identity property: )

                       (Add: )

The equation of line is .