The distance between any two points is the so-called distance formula which is an extension of the Pythagorean Theorem:
d^2=(x2-x1)^2+(y2-y1)^2, where (x1,y1) and (x2,x1) are two points.
In this case:
d^2=(3--6)^2+(5--6)^2
d^2=9^2+11^2
d^2=81+121
d^2=202
d=√202 units
d≈14.21 units (to the nearest hundredth of a unit)