When the center of earth is 2 × 1011 meters from the center of mars, the force of gravity between the two planets is about 64.32 × 1014 newtons. the mass of earth is about 6 × 1024 kilograms, and the mass of mars is about 6.4 × 1023 kilograms.?

I calculate it as 6.407 x 10^15 newtons. 
Your answer is 6.432 x 10^15 newtons so I'd say that's an accurate calculation.

When rates are expressed as a quantity of 1, such as 2 feet per second or 5 miles per hour, they are called unit rates. if you have a multiple-unit rate such as 120 students for every 3 buses, and want to find the single-unit rate, write a ratio equal to the multiple-unit rate with 1 as the second term.