(a + 3) * (B + 3) - AB = 54, then what is ab equal to

(a + 3) * (B + 3) - AB = 54, then what is ab equal to

(a+3)*(b+3)-ab=54
It unfolds well
ab+3(a+b)+9-ab=54
be
3(a+b)+9=54
a+b=15