I have stopped going to school due to my mental break downs because of school so my teachers started sending me my work i have missed but the only thing i was not at school to learn how to do it so please help me....!!

Answer:
1 - c 6.4 Ă—10^6
2 - a 6.4 Ă—10
3- b 6.04 Ă—10^5
4) 5.21Ă— 10^8 Ă— 1.6km
=8.33Ă—10^8 km
5) 10,000,000,000 = 1 Ă—10^10
BRAINLIST PLS