It is better to write the two numbers in the exponential form because writing too many zeros can become a headache and chances of writing more or less number of zeros increases.
107 x (8 x 1013) = 8 x 107+13 = 8 x 1020
80000000000000
10000000. Anything times 1 equals itself
10000000 x 288888888 = 288888888000000
10000000 x 54750 = 547500000000
80000000000000
The answer is 170,080,000,000
100000000000000
The answer to your equation is 100,000,000,000,000,000
10000000
10,000
10000000x99999 = 999990000000
10000000