Compute pH of the saturated solution of La(OH)3 in ther 3x10^-5 M aqueous solution of La(NO3)3xKsp(La(OH)3).
...........La(OH)3 ==> La^3+ + 3OH^-
.............x...........x......3x
La(NO3)3 ==> La^+3 + 3NO3^-
.............3E-5M...3*3E-5M
Ksp = (La^3+))OH^-)^3 = ?
Substitute into Ksp and solve for x.
Note that you have two sources for La; i.e., (x) from La(NO3)3 and 3E-5 from La(NO3)3.
Since x = (OH^-) you will need to convert to pH.