Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| No. in series | No. in season | Title | Directed by | Written by | Original air date | Production code | U.S. viewers (million) |
| --- | --- | --- | --- | --- | --- | --- | --- |
| 34.0 | 1.0 | "Hats and Bats" | Christopher Chulack | Jonathan Lisco | February13,2013 | 3X7551 | 1.16 |
| 35.0 | 2.0 | "Heat" | Daniel Sackheim | Heather Zuhlke | February20,2013 | 3X7552 | 1.21 |
| 36.0 | 3.0 | "Babel" | J. Michael Muro | Aaron Rahsaan Thomas | February27,2013 | 3X7553 | 1.18 |
| 37.0 | 4.0 | "Under the Big Top" | Felix Alcalá | Sara Gran | March6,2013 | 3X7554 | 1.51 |
| 38.0 | 5.0 | "Off Duty" | Regina King | Zack Whedon | March13,2013 | 3X7555 | 1.72 |
| 39.0 | 6.0 | "Bleed Out" | Christopher Chulack | Chad Feehan | March20,2013 | 3X7556 | 1.45 |
| 40.0 | 7.0 | "Heroes" | J. Michael Muro | Heather Zuhlke | March27,2013 | 3X7557 | 1.32 |
| 41.0 | 8.0 | "The Felix Paradox" | Stephen Cragg | Aaron Rahsaan Thomas | April3,2013 | 3X7558 | 1.46 |
| 42.0 | 9.0 | "Chaos" | Christopher Chulack | Zack Whedon | April10,2013 | 3X7559 | 1.59 |
Question:
Who wrote the episode that has a production code 3x7557?
Answer:
Heather Zuhlke