When exchange fees widen the spread
A stock is bid, offered, so the mid is and the half-spread is cent. The exchange runs a maker-taker fee schedule: it charges a taker fee of cents per share to anyone who crosses, and pays a maker rebate of cents per share to anyone who provides a resting order that gets filled.
What does it truly cost to cross versus to provide? What is the round-trip cost if you take both legs?
Show a hint
Add the fee to, or subtract the rebate from, the half-spread. Both are measured against the mid.
Your answer
This one is open-ended. Work it through, then check your reasoning against the full solution.