Question 597170
Log2 (10)=x 
Log12 (1243)=x 
----
Change of base Formula: log(Base A)B = [log(base C)B] / [log(base C)A]
Note: The "C" can be any positive number.
---
Your Problems: 
x = log(10)/log(2) = 1/0.3010 = 2.3219
---------------
x = log(1243)/log(2) = 10.2796
==================================
Cheers,
Stan H.