tolong dijawab dengan cara

{ n (n+1)(n+2) }/3
n = 1 => {1(1+1)(1+2) }/3= (1.2.3)/3 = 2
n = 2=> { 2(2+1)(2+2)}/3 = (2.3.4)/3=8
n=3=> {3(3+1)(3+2)}/3=(3.4.5)/3=20
n=4=>{4(4+1)(4+2)}/3=(4.5.6)/3=40
n=5=>{5(5+1)(5+2)}/3=(5.6.7)/3=70
Jumlah = 2+8+20+40+70= 140