I'm not exactly a geek at math and measurements is one of the things i have always messed up at.
anyone mind me?

Check the picture below.

well, √180 is about 13.4, and √72 is about 8.5, clearly 2*8.5 ≠ 13.4.

< coa = 150 ( given)

as ba and bc are tangents

so oc and oa is perpendicular to cb and ab respectively because in circle normal passes through centre

so in quadrilateral oabc

< coa + < oab + < ocb + < abc = 360

150 +90+90 + < abc = 360

330 + < abc = 360

< abc = 360 -330 = 30

so < abc = 30

⭐dhruv⭐