How do i solve my son is in 5th grade? ?

1)
?×1/10=7.34
?=10×7.34
?=73.4

2)
8.64×?=0.864
?=0.864/8.64
?=864/8640
?=1/10=0.1

3)
?×100=69.4
?=69.4/100
?=694/1000
?=0.694

4)
790×?=79,000
?=79,000/790
?=100

5)
?×1/100=570
?=100×570
?=57000

6)
0.0064×?=6.4
?=6.4/0.0064
? =64000/64
?=1000

Ithink is a. true, but not sure