Example 4 (Index Equation – Substitution) June 15, 2018February 4, 2014 by Example 4Solve each of the following.(a) ${3}^{x-1}+{3}^{x}=12$ (b) ${2}^{x}+{2}^{x+3}=72$ (c) ${4}^{x+1}+{2}^{2x}=20$