GMAT Question of the Day – PS- Exponents 1

GMAT Question of the Day – Problem Solving – Exponents

If m and z are integers and if ${{21}^{2m}}{{9}^{4m+2}}={{3}^{z}}{{7}^{4}}$ , what is the value of m + z?

A. 8

B. 14

C. 20

D. 24

E. 26

[spoiler]E.[/spoiler]