What is the answer to (4-i)(6-5i) ?

For this we must use foil and multiply
4*6
4*-5i
-i*6
-i*-5i
to get (respectively to above)
24
-20i
-6i
5i^2
combine all of those to get:
24-26i+5i^2
now, i squared is equal to -1, so we can simplify the above even further:
24-26i+5(-1)
24-26i-5
19-26i
Now, that would be your final answer. But if you want it in radical form you would get this: (just so you know, i is the square root of -1, or an imaginary number)