tolong bantu jawab kak

a. Sn = n/2 × [2a + (n-1)]× b
=4/2 × [2×2 + (4-1)] ×4
= 2 × (4+3) × 4
=2 × 7 ×4 = 56

b. Sn = n/2 × [2a + (n-1)]
= 35/2 × [2.2 + (35-1)] × 4
= 17,5 × (4 + 34) × 4
=17,5 × 38 × 4
=2660