Question 1193713
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There isn't enough information. We're not given how long the loan duration is. 


However, as an example, let's say the timeline is exactly 1 year
Let's calculate the simple interest
i = P*r*t
i = 4000*0.15*1
i = 600
The $600 is the interest to be paid on top of the original $4000 borrowed.


The total cost would be 4000+600 = 4600 dollars only if the loan payback duration is 1 year. The answer of course would be different for another value of t.
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