Answer:
x^18, or x¹⁸
Explanation:
8¹⁵/8⁻³
8¹⁵ ₓ 8³
8¹⁸
When an exponent is negative, you have to flip what the exponent is attached to. If the negative exponent is the numerator(x⁻¹/1), it becomes a denominator(1/x¹). If the negative exponent is in the denominator (1/x⁻¹), it becomes a numerator(x¹/1).