Question

\[2^{x} \times 4^{x} \times 8^{x+1} = 2^{21}\]

Answer 1

Remember some properties of exponents:

\[(ab)^n = a^nb^n\]\[a^n*a^m = a^{n+m}\]

Answer 2

The entire left side can be written as a product of powers with 2 as base. Since they are all multiplied together, keep base of 2 and add the exponents.
Then if a^m = a^n, it must be that m = n.