Verified answer

21⁶ * 7⁶ / (7¹⁰ * 9³) = (7*3)⁶*7⁶ / (7¹⁰*(3²)³) = 7⁶*3⁶*7⁶ / (7¹⁰*3⁶) = 7⁶⁺⁶⁻¹⁰ * 3⁶⁻⁶ = 7²*3⁰ = 49

(a^m)^n = a^(mn)

a^0=1

a^m*a^m = a^(m+n)