On a piece of paper, use a protractor and a ruler to construct △abc with ab=6 cm , m∠a=80° , and m∠b=50° .
what is ac ?
3 cm
6 cm
9 cm
12 cm

We know that the summation of angles of a triangle is 180°. Then we find angle of C by,
m∠A + m∠B + m∠C=180° 
80° + 50° + m∠C=180°
m∠C=180°- 80°+ 50° 
m∠C=50°
Since we now angle of C, we can use Sine Law in solving for AC
sinC/AB=sinB/AC
sin50°/6 =sin50°/AC
AC=6cm
Therefore, AC is equal to 6cm.

I'm pretty sure it's b). i try drawing the functions out and b is the one that stands out or isnt a "line"