f.4 app. of diff

1)
http://i729.photobucket.com/albums/ww291/kaka1307/DSC00533.jpg
an antheletic field of perimeter P m is composed of a rectangle BCEF
with area 7000 m and 2 semi-cirlcles FAB and CDE.Let x m and 2r be the length and width of the rectangle BCEF respectively.
a)espress P in terms of r.
b)find the values of x and r so that P is a minimum.


2)
http://i729.photobucket.com/albums/ww291/kaka1307/DSC00534.jpg?t=1273914571

A rectangle DBFE is inscribed in triangle ABC with angle ABC=90
it is given that AB=12 cm,BC=9 cm,DE=x m and EF=y cm
a)show that 36-4x/3
b)find the minimum area of the rectangle DBFE.

ans: 1a)P=2(pi)(r)+7000/r
1b) r=33.38, x= 104.86
2b) 27cm


I want to ask both 1b & 2b only.
pls show clear steps.