What is 345*90 answer.

31,050.

Calculators could be used to get that (if allowed) or you could just do it out on paper.

345

x90

000

31,050

I got this answer by multiplying 345 times the 0 in 90, and then multiplying 345 times the 9 in 90, but I added a zero at the end of it.

31,050 (345 x 9, then put a zero on the end)