\( \frac{7}{8} \) of a number = 78.75. The number is the whole.

• \( \frac{7}{8} \times \text{number} = 78.75 \)
• \( \text{number} = 78.75 \div \frac{7}{8} = 78.75 \times \frac{8}{7} \)
• \( 78.75 \times 8 = 630 \)
• \( 630 \div 7 = 90 \)

Final Answer: 90