The formula for calculating the distance between two points is:
#d = sqrt((color(red)(x_2) - color(blue)(x_1))^2 + (color(red)(y_2) - color(blue)(y_1))^2)#
Substituting the values from the points in the problem gives:
#d = sqrt((color(red)(6) - color(blue)(4))^2 + (color(red)(-2/3) - color(blue)(2))^2)#
#d = sqrt((color(red)(6) - color(blue)(4))^2 + (color(red)(-2/3) - (3/3 xx color(blue)(2)))^2)#
#d = sqrt((color(red)(6) - color(blue)(4))^2 + (color(red)(-2/3) - 6/3)^2)#
#d = sqrt(2^2 + (-8/3)^2)#
#d = sqrt(4 + 64/9)#
#d = sqrt((9/9 xx 4) + 64/9)#
#d = sqrt(36/9 + 64/9)#
#d = sqrt(100/9)#
#d = sqrt(100)/sqrt(9)#
#d = 10/3#