for this question you can say:
5/9( °F - 32) = -10 °C
so now you should solve the equation:
5F/9 - 160/9 = -10
⇒ 5F/9 = -10 + 160/9 ⇒ 5F/9 = -90/9 + 160/9 ⇒ 5F/9 = 70/9 ⇒ now you can multiply both sides of the equation by 9 so you will have:
5F = 70 ⇒ F = 14 ° F :)))
i hope this is helpful
have a nice day