From the curve of the normal distribution with the mean of 250 grams and 
the standard deviation of 20 grams, we should find z-score in a way, 
that the area under the curve on the right of the z-score would be 4%.


So, go to website

https://davidmlane.com/hyperstat/z_table.html

and use free of charge online calculator, specially developed for such tasks.

    (Use it in the mode "Value from an area").


In the calculator ports, assign these input parameters

    Area 0.04

    Mean  250

    SD      4


    Option: Above.


Then press "Recalculate" button  and get the number 285 grams  (rounded to the nearest gram).


It is the answer to the problem's question.


Alternatively, you may use the standard function invNorm in your regular calculator TI-84

                prob.  mean SD    <<<---===  formatting pattern
    P = invNorm(0.96,  250, 20).


You will get the same answer  P = 285 grams  (rounded to the nearest gram).