79.9 times 100= 7990 divide by 99= 80.7070707 is this right

Right

yes one could say though if you are into arithmetic and geometric sequences

80 + 70/100 + 70/10,000 ....
80 + .70 + .70/100 +.70/100^2 + .70/100^3 ..
= 80 + .70(1/.99) geometric sequence sum

To verify if your calculation is correct, let's follow the step-by-step process:

79.9 multiplied by 100 equals 7990.
7990 divided by 99 equals 80.9090909 (rounded to seven decimal places).

You were close, but the correct answer is 80.9090909.