The best thing to do is to use the whole number as 7, as if you go lower than this, it will become a decimal.
70000/7= 10000
Therefore, you can have 7 multiplied by 10000.
You then need to find out what the power of 10 for 10000 will be.
You can do this by continually dividing it by ten, until you get back to ten.
10000/10= 1000/10=100/10=10.
You've got three lots, and then you have to add one, giving you the power of 4.
Another way that 70000 can be written is 7x10 to the power of 4.
Hope this helps :)