Find the resultant of three forces- F13i-4j 2kF22i 3j-kF32i 4j-5k?

Assuming you mean:

F1 = 3i - 4j + 2k,

F2 = 2i + 3j - k,

F3 = 2i + 4j - 5k.

Simply add all of them algebraically, i.e. add i's to i's, j's to j's etc. - this works in all dimensions.

The resultant force F will be in your case:

F = 7i + 3j - 4k.