If I understand this correctly, you extend AB to x and extend AC to y
When connecting a line between x and y two angles form
Angle BXY is 62
Angle AYX is 51
Adding 62+ 51=113
180-113=67 which is measure of angle A
Now you can use the Law of Cosines to derive side BC which I will call side a since it is across from angle A
a^2=b^2+c^2-2bccosA
a^2=6^2+9^2-2(6)(9)cos 67
a^2=36+81-108cos67
a^2=117-108cos67
Take square root both sides
a = 8.65