A burger shop's marginal product of labour, measured as the number of burgers produced per week, is MP_L = 55 - 5L, where L is the number of employees. The average price of a burger in this perfectly competitive market is $10. The burger shop can hire employees at $300 per week. What is the marginal product of the fourth employee?

(Only include numerical values in the answer field. Do not include any text orsymbols, such as $, %, etc.)