Hello there! So, by looking at the numbers, there are eighteen tens being compared to 21 * (5 + 5). Eighteen tens is equivalent to 180, because tens = 10, and 18 * 10 is 180. To solve 21 * (5 + 5), we first add what's in the parenthesis. 5 + 5 is 10. 21 * 10 is 210. And as we see, 180 < 210, because the one in the hundreds place is less than the two in the hundreds place. The answer is eighteen tens < 21 * (5 + 5).
