To find the distance between two points, use the distance formula, which is sqrt[(ysub2-ysub1)^2+(xsub2-xsub1)^2].
Substitute the coordinates in so you have:
d=sqrt{[4-(-8)]^2+[1-(-2)]^2}
d=sqrt(12^2+3^2)
d=sqrt(144+9)
d=sqrt153
d=3sqrt17=approx. 12.369
