tolong dong no 6,7,8,9

6. 2√15 × √6 : √5
= 2√90 : √5
= 2√18
= 6√2 (D)

7. 9/12 × x/100 × 800.000 = 920.000 - 800.000
3/4 × 8.000x = 120.000
6.000x = 120.000
x = 120/6
x = 20% (C)

8. 20% = 100% × (420.000 - x) / x
20x = 42.000.000 - 100x
120x = 42.000.000
x = 4.200.000/12
x = 350.000 (B)

9. Rumus : 1/2 n(n + 1) - 11
Ke-5 = 5/2 (5 + 1) - 11
Ke-5 = 5/2 (6) - 11
Ke-5 = 15 -11
Ke-5 = 4

Ke-6 = 6/2 (6 + 1) - 11
Ke-6 = 3(7) - 11
Ke-6 = 21 - 11
Ke-6 = 10

(D) 4, 10