Explanation

a^4 x a^8 x a^3 =?

a^4 has an exponent of 4.

a^8 has an exponent of 8.

a^3 has an exponent of 3.

Add the exponents together: 4 + 8 + 3 = 15.

Therefore, a^4 x a^8 x a^3 simplifies to a^15.