SOLUTION: <a href="http://tinypic.com?ref=245fymc" target="_blank"><img src="http://i40.tinypic.com/245fymc.jpg" border="0" alt="Image and video hosting by TinyPic"></a>
Algebra.Com
Question 572185: 
Answer by jim_thompson5910(35256) (Show Source): You can put this solution on YOUR website!
A = ab*sin(theta)/2
13 = 7b*sin(60)/2
13 = 7b*(sqrt(3)/2)/2
13 = 7b*(sqrt(3)/4)
13*4 = 7b*sqrt(3)
52 = 7b*sqrt(3)
52/(7*sqrt(3)) = b
b = (52*sqrt(3))/21
So the answer is 
RELATED QUESTIONS
(answered by jim_thompson5910)
(answered by ankor@dixie-net.com)
(answered by mananth)
(answered by MathLover1)
(answered by ikleyn)
(answered by Fombitz)
(answered by josgarithmetic,math_helper)
(answered by algebrahouse.com)
(answered by Alan3354)