exam Maths Puzzle Numerical Ability

Write your result in scientific notation. (2x10^5)(4x10^4) This is what I have done so far: (2x2^5*5^5)(4x2^4*5^5). I know the answer is suppose to be 8x10^9, I can not figure out how to show the rest.

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exam Other Question

At 9 pm, Lucy started to gallop her horse at 20 miles per hour to catch Edmund, who had a three hour head start, and if Lucy was still 30 miles behind at 11 om, how fast was Edmund riding? (9x+3)/(x^2-9) - (5)/(x-3) Any help with this problem would be appreciated.
Thanks Rhee