how many times larger is 10 to the 18th power 20 times then 10 to the -18th power

To have 10^18 twenty times, you have 10^18 x 20, which is 20 x 10^18  or 2 x 10^19.

You want to find the number that, when multiplied to 10^-18 will give you 2 x 10^19

Equation:  10^-18 · x  =  2 x 10^19

Divide both sides by 10^-18:          x  = 2 x 10^19 ÷ 10^-18

When you divide numbers with the same base, subtract the exponents:

                                                    x  =  2 x 10^(19 - -18)

                                                    x  =  2 x 10^37.

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