2121 base 3 = 106 base b. Solve for b

Suggest you use the following procedure:

1. Convert 2121 base 3 to base 10.

2. 106 in base b is equal to 1*b^2 + 0*b +6. So set this equal to the base 10 number you found in step 1, and solve for b.

Post back if you still have a problem with this.