Let A be the sum of the first 20 terms and ' B ' be the sum of the first 40-  terms of the series 12+2.22+32+2.42+52+2.62+.. If B−2A=100λ then λ is

B-2A=∑n=140an-2∑n=120an=∑n=2140an-∑n=120anB-2A=212+2.222+232+...+402−12+2.22+32+2.42+...+202=20(22+2.24+26+2.28+..+60)=20{(22+24+26+..+60)⏟20 terms+(24+28+..+60)⏟10 terms}=20202(22+60)+102(24+60)=10(20.82+10.84)=10(1640+840)=100(164+84)=100×248→λ=248