Write 12345678 x 10^-9 as a decimal.

Since it's multiplied by 10 to the negative 9, we go back 9 places. 
Normally since the decimal point is at the end like this,
12345678.0
we just have to move it to the left 9 spots.
That gives us:
.012345678
Hope this helps!

That is 12345678 * 0.000000001

=  0.012345678

The answer is 15×7=105therefore, 105×5=525 miles