5^9 * 10^21 / 5^29 * 4^10 = ?

5⁹*10²¹/(5²⁹*4¹⁰)=5⁹*5²¹*2²¹/(5²⁹*2²*¹⁰)=5⁽⁹⁺²¹⁾*2²¹/(5²⁹*2²⁰)=5³⁰*2²¹/(5²⁹*2²⁰)=

=5⁽³⁰⁻²⁹⁾*2⁽²¹⁻²⁰⁾=5¹*2¹=10.