Answer:
5.87 x

Explanation:
You need to write the number as 1 or larger than 1, but less than 10. That means that I need to put the decimal between the 5 and the 8. Now I have to count how many places I moved the decimal. I think that I counted right. It was moved 17 places. Since the number in standard form is much smaller than 5.87, the exponent will be negative.