Question 1166996
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            I came to bring a correct/(corrected) solution.



<pre>
let x equal the number of days for the rental.
let y equal the total cost.


your equations are:


y = 1000                for 0 <= x <= 3         (1)

y = 1000 + 400 * (x-3)  for x > 3               (2)


if the number of days of the rental is less than or equal to 3 days, use the first equation.


if the number of days of the rental is more than 3 days, use the second equation.
</pre>


Look into my solution attentively and find the difference with the solution by @Theo.