80
7 tens and 20 ones is 7 × 10 + 20 × 1 = 70 + 20 = 90 (ninety).
10 or 5
99
yes
310
9,870
The number that is 2 tens (or 20) more than 71 is 91.
13 tens is the same as 13 x 10 which equals 130.
Tens of quintillions.
20 and 30
2 tens, which is twenty.