First you'd find angle C as it is opposite the side AB that you want to find
But to find angle c you first have to find angle A using the soh
Then you'd do 180 - (90 + angle A) =angle C as angles in a triangle add up to 180
Then you'd use the soh using angle A and 12 to find side AB
Working out
Sin(x)=12/7
Sin-1(7/12)
=35.685
180- (90+35.685)
=54.315
Sin(54.315)=o/12
Sin(54.315)*12
=9.746794345