1.0*10-15divided by 4.2*10-7

1 x 10 - 15 / 4.2 x 10 - 7

Due to order of operations you have to do do the multiplication and division first, from left to right.

So start with 1.0 x 10. This = 10.

Then you have to skip over the subtraction for now. Multiply 15 by 4.2. This equals 63. Then multiply this by 10, so 630.

Then rewrite the equation. It's 10 - 630 - 7. Then just subtract. 10 - 630 = - 620.

-620 - 7 = - 627. (Two subtracts make an add)

-627 is your answer