Question

add the product of 9 and 9 to 90

Answer 1

9×9=81
now add 81 to 90
then we get 171

Answer 2

Sum = 10/2[2*9 + (10-1)*9]
= 5[18 + 9*9]
= 5[18 + 81]
= 5[99]
= 495