p(x,y)=1800x^.621*y^.379

a.) find number of units produced with x labor and y unity of capital
answer: i got 3888064

b. marginal productivies
answer i got: Px = -4749x^-.379*y^.379
Py = -118x^.621*y^-.621
c.) estimate productiives at x=2500 and y 1700
i got: Px=-4103
Py=-1421

I am NOT sure if i did everything correct and if i did something wrong, can someone help me???