A/B ==2/5,

B/C ==5/3,

A+B+C==60, solve for A, B, C

A==12 kg, B==30 kg, C==18 kg

Grade B==7/kg

Grade A==7/kg - 2==5/kg

Grade C==7/kg + 3==10/kg

B==7/kg x 30 kg==210 - Grade B pears

A==5/kg x 12 kg ==60 - Grade A pears

C==10/kg x 18 kg==180 Grade C pears

So: A : B : C ==60 : 210: 180==2 : 7 : 6 [Their ratio by the number of pears in all 3 grades]