Any idea? Very confused.

Her total depth will be the sum of those numbers, and they seem to want it with a negative sign so we give it to them that way.
[tex]17 \frac 2 3 + 9 \frac 3 8 = (17+9) +(\frac{16}{24} + \frac{9}{24}) = 26+\frac{25}{24} = 27 \frac{1}{24}[/tex]
First answer.