What is a trick for multiplying 9`s

A trick that is good for multiplying 9's is, remember that each time the tens digit changes the number in the ones spaces minuses 1. If you don't understand what I am saying look at the following:- 

9
18
27
36
45
54
63
72
81

See the pattern? In the tens place you need to add 1 and in the tens place you need to subtract by 1.

Hope I helped ya!! xD

 This works for 9 times 1 through 9 times 10. You can take the number that is times 9 and and minis the number by one. Then you think about what number plus the first number ( the number that is times 9 and and minis the number by one) equals 9 and that number goes in the tens place. If you don't understand then look at this:
9×1=09
9×2=18
9×3=27
9×4=36
9×5=45
9×6=54
9×7=63
9×8=72
9×9=81
9×10=90

4038 is the answer lol just use a calculator