First thing I see is that we can take 12 out of both of them, that's helpful.
a2 is 1, a4 is 4.
2^0 is 1, and 2^2 is 4, that's a helpful fact... but our subscripts were 2 and 4, not 0 and 2. We could shift them by using 2^(x - 2). Thus:
\(12 * 2^{x-2}\)
I suppose 2^x * 2^-2 is basically 2^x / 4, so we could simplify further to:
\(3 * 2^{x}\)
