Since the problem is 2x^2-5xy-y^3 we first have to plug in what the x and y stands for, once you do that your problem should look like this:
2(-3)^2- 5(-3)(-2)- (-2)^3
Now take the parentheses away and when you do that your signs change.
2x3^2-5x(-3)x(-2)-(-2)^3
do it again with -5x(-3)x(-2)
2x3^2-30-(-2)^3
now do this with (-2)^3
2x3^2-30-(-8)
Now evaluate the power
3^2 becomes 9
2x9-30-(-8)
then change -(-8) to a positive since two negatives make a positive
2x9-30+8
Now multiply the numbers 2x9
18-30+8
Then do 18-30 which equals -12 then add 8
Now you are left with your answer:
-4
Hope this helps! :3