Problem B3::

thetaa1,theta2,theta3,theta4 are measured with respect to HORIZONTAL,
To solve for theta1, theta2,theta3,theta4, we formulated the equations:

15*cos(theta1)+15*cos(theta2)=2.5
15*sin(theta1)+15*sin(theta2)=12
20+15*cos(theta3)+15*cos(theta4)=7.5
15*sin(theta3)+15*sin(theta4)=12

To solve them, write in Matlab:

>>syms a b c d;
>>[a,b]=solve('15*cos(a)+15*cos(b)-2.5,15*sin(a)+15*sin(b)-12',a,b)

a =
 
-225.97915955848346029761057905952
 
 
b =
 
96.763069982922402736391895262231

>>[c,d]=solve('15*cos(c)+15*cos(d)+12.5,15*sin(c)+15*sin(d)-12',c,d)

c =
 
-224.77309325855220912285668033374
 
 
d =
 
97.579401449538659138005079990949
 

The answer is in radians. 
The answer in degrees is
therefore 	theta1=143.9
		theta2=12.3
		theta3=81.6
		theta4=190.9