Let's denote the number of days Adam works in a month as \( d \).
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Cost of renting in the city (including walking to work):
- Total cost = $615 per month
-
Cost of renting in the suburbs (including train fare):
- Rent = $500 per month
- Daily train cost = $5 per day
- Total train cost for \( d \) days = \( 5d \)
- Total cost = \( 500 + 5d \)
To find out how many days \( d \) make these two options equal in cost, we set the total costs equal to each other:
\[ 615 = 500 + 5d \]
Now, we can solve for \( d \):
- Subtract 500 from both sides:
\[ 115 = 5d \]
- Divide both sides by 5:
\[ d = \frac{115}{5} = 23 \]
Thus, Adam has to work 23 days per month for the costs of both renting options to be equal financially.