ba tu donk no.4 nihh.. susah

tali dipotong 5 barisan aritmatika
terpendek = 4 m = a
terpanjang = 16 m = U5

jumlah semua tali = ...

rumus:
Sn = n/2 (a + Un)
S5 = 5/2 (4 + 16)
= 5/2(20)
= 5 × 10
= 50 meter