You have the correct x and y values. Nice work.
x/3 = 3/4
x*4 = 3*3
4x = 9
x = 9/4
AC = AD+DC
AC = 4+x
AC = 4+9/4
AC = 16/4 + 9/4
AC = 25/4
AB^2 + BC^2 = AC^2
5^2 + y^2 = (25/4)^2
25 + y^2 = 625/16
y^2 = 625/16 - 25
y^2 = 625/16 - 400/16
y^2 = 225/16
y = sqrt(225/16)
y = 15/4
