I'm not sure if the answer is right, but here you go.
y=mx+b
'm' is for gradient of the line. First, calculate the gradient.
Let's use (6,15) and (8,21)
Gradient, m = [tex]y_{2} [/tex] - [tex] y_{1} [/tex]
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[tex] x_{2} [/tex] - [tex] x_{1} [/tex]
= 21 - 15 = 6 = 3
----------- ----
8 - 6 2
Therefore, m = 3 . Now let's search 'b' .
Let's use (6,15) again. Substitute it into the equation.
y=mx+b
15 = 3 (6) + b
b = -3
Thus, the equation : y=3x -3
