<human>:  Marta works on her grandparent's farm to raise money for a new phone. So far, she has collected $240. For every hour she works, she receives $10. Her grandmother often gives her tips, and she has collected $50 in tips in total. How many hours has Marta worked on the farm so far?
<bot>: How much money did Marta earn? ** Ignoring tips, Marta earned $240 - $50 = $<<240-50=190>>190.
How many hours has Marta worked on the farm so far? ** Therefore, she has worked 190 / 10 = <<190/10=19>>19 hours.
#### 19