.68
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There is no solution since they are both adding $10 to their accounts every week.
<u>The angle based on the diameter is always right</u>
Then <ABC=90 and ∠BAC=∠ACB=45° ; and ∠BCD=180-45=135 then x=(180-135):2=22,5°
C can be found using pythagoras theorem. c2=a2+b2. Now, b is not given, but we know that cos(theta)=b/c=>b=c*cos(theta). Substituting b in the above relation, c2=a2+c2(cos(theta))^2=>c2=a2/(1-cos((theta))^2). c is the squareroot of c2. Hence c=sqrt(2/(1-cos((theta))^2))