Change 121 base three to base ten.

To convert 121 base three to base ten, we can use the following formula:

(1 * 3^2) + (2 * 3^1) + (1 * 3^0) = 9 + 6 + 1 = 16

Therefore, 121 base three is equal to 16 in base ten.

$$121_{\three}=1\times3^2+2\times3^1+1\times3^0=9+6+1=16$$