Diketahui rumus barisan aritmatika un=3n+4 maka tentukan 40 suku pertama

Tolong bantuannya ,jadikan jawaban saya sebagai jawaban terbaik

U1 = 3 + 4 = 7
U2 = 6 + 4 = 10
U3 = 9 + 4 = 13
U4 = 12 + 4 = 16
U5 = 15 + 4 = 19
U6 = 18 + 4 = 22
U7 = 21 + 4 = 25
U8 = 24 + 4 = 28
U9 = 27 + 4 = 31
U10 = 30 + 4 = 34
U11 = 33 + 4 = 37
U12 = 36 + 4 = 40
U13 = 39 + 4 = 43
U14 = 42 + 4 = 46
U15 = 45 + 4 = 49
U16 = 48 + 4 = 52
U17 = 51 + 4 = 55
U18 = 54 + 4 = 58
U19 = 57 + 4 = 61
U20 = 60 + 4 = 64

U1 = 3+4 = 7
U40 = 120 + 4 = 124 
jumlah 40 suku pertama 
1/2 x 40 x (124+7) = 2620
20 x 131 = 2620