The change in x, as we move from left to right, is 7-4, or +3.
The corresponding change in y is -2i-2i = -4i.
Use the Pythagorean Theorem to find the length of this line segment:
d = distance from 4+2i to 7-2i= sqrt( [3]^2 + sqrt( [-4]^2 ) = sqrt(9+16) = 25 (ans.)