The distance between the points (x₁,y₁) and (x₂,y₂):
\(d=\sqrt{(x_2-x_1)^2+(y_2-y_1)^2}\)
\((-10,3) \\
x_1=-10 \\ y_1=3 \\ \\ (-10,12) \\ x_2=-10 \\ y_2=12 \\ \\
d=\sqrt{(-10+10)^2+(12-3)^2}=\sqrt{0+9^2}=\sqrt{9^2}=9\)
Another method:
The points have the same x-coordinate so they lie on the same line. y-coordinates are positive so you just subtract 3 from 12. See the picture in the attachment.
The answer is 9.
