Please help me with calculus problems! 10pts!

http://www.flickr.com/photos/caramelvip/6974067746/

http://www.flickr.com/photos/caramelvip/7120145105/

The first question, f(x)=sqrt(25-x^2) and b=5
The second question, -3 (5-5-3=-3) and 21 (3*5+3*(4-2)=21)