The slope -intercept form of linear equation is y=mx+b.
Where m= slope and b=y-intercept.
Formula to find m is,
m=\frac{y_{2}-y_{1}}{x_{2}-x_{1}}
The line passes through (-2,3) and (-2,6).. So, we can plug in x1=-2, y1=3, x2=-2 and y2=6 in the above formula. So,
m=\frac{6-3}{(-2)-(-2)}
m=\frac{3}{-2+2}
m=\frac{3}{0}
Since 0 is at the denominator so, m= undefined because there is no change in x. Whatever be the values of y but x will also be -2.
So, the equation will be x=-2.