Bantu ya semua... U2+U4=52 U1=8 U21=?

U2 + U4 = a+(n-1)b + a+(n-1)b
52 = 8+(2-1)b + 8+(4-1)b
52 = 8+b+8+3b
52 = 16+4b
36 = 4b
b = 9

U21 :
= 8+(21-1)9
= 8 + 180
= 188