Answer:
3 x 10^18 kg
Step-by-step explanation:
Time period, T = 3 days = 86400 x 3 = 259200 seconds
r = 7 x 10^5 m
Let M be the mass of planet
Use the formula of time period of satellite
![T = 2\pi \sqrt{(r)/(GM)}](https://img.qammunity.org/2020/formulas/physics/high-school/6zk744m01c0vpf9q6vr6uit9q6gfme9ujz.png)
Where, G be the universal gravitational constant.
![M=(4\pi ^(2)r^(3))/(GT^(2))](https://img.qammunity.org/2020/formulas/physics/high-school/ijsv6l7fiuv9dca2na4hgjyagags1k1l79.png)
By substituting the values
![M=(4* 3.14 * 3.14* \left ( 7* 10^(5) \right )^(3))/(6.67* 10^(-11)* 259200* 259200)](https://img.qammunity.org/2020/formulas/physics/high-school/10o4hfmzyyc65ro7xfd5vy87g9xbltr478.png)
M = 3 x 10^18 kg
Thus , the mass of planet is 3 x 10^18 kg.