What is the concentration (in m of hydroxide ions in a solution at 25.0 °c with ph = 4.282?

First, you can calculate the [H+] concentration.

[H+] = 10^-pH

[H+] = 10^-4.282 = 5.22 x 10-5

then use this formula to solve for [OH-] concentration--> [H+] x [OH-] = 1.0x 10-14

(5.22x10-5) x [OH-] = 1.0x10-14

[OH-] = 1.92 x 10-10