Insulin contains two poly peptide chains contains ‘x’ and  ‘y’ number of aminoacids respectively  and possess ‘z’ number of disulphur bonds .Then y-x+z will be----------

$x=21,y=30,z=3y-x+z=30-21+3=12$

Insulin is composed of two peptide chains referred to as the A chain and B chain. A and B chains are linked together by two disulfide bonds, and an additional disulfide is formed within the A chain. In most species, the A chain consists of 21 amino acids and the B chain of 30 amino acids.