3200 plus 1800 is 5000.
So find the percentage of 5000 1800 is.
So 36%
You want to find the value of x for which the area under the curve to the left of x is 0.6. One way to do that is to create the cumulative distribution function (CDF) for the given PDF, then see where it is equal to 0.6.
Doing that, we find a = 5.