Answer:
![F=18.58* 10^(-11)\ N](https://img.qammunity.org/2020/formulas/physics/college/v4saxd5wdjs74w7p2fp1x64x000um351at.png)
Step-by-step explanation:
Given:
mass of first particle,
![m_1=6.7\ kg](https://img.qammunity.org/2020/formulas/physics/college/tnwoota7qhh966pbd97vyiuorp1i4xddl2.png)
mass of second particle,
![m_2=5.1\ kg](https://img.qammunity.org/2020/formulas/physics/college/aertrwosizhtke72i5vkv7g8dev2gickq1.png)
mass of third particle,
![m_3=3.7\ kg](https://img.qammunity.org/2020/formulas/physics/college/owdx3wzw6mdokhgxpdjhpevu1puop0n6x6.png)
coordinate position of first particle in meters,
![(x_1,y_1)\equiv(4.2,0)](https://img.qammunity.org/2020/formulas/physics/college/toe2fhdkfoqeo8c9pna63ivwqvybcibkmf.png)
coordinate position of second particle in meters,
![(x_2,y_2)\equiv(0,2.8)](https://img.qammunity.org/2020/formulas/physics/college/97xw02cajtqy2dym7y1kt3oey58t26z9gx.png)
coordinate position of third particle in meters,
![(x_3,y_3)\equiv(0,0)](https://img.qammunity.org/2020/formulas/physics/college/zxtz1re2a9hzp5f50r12du0anyqsxztmrs.png)
Now, gravitational force on particle 3 due to particle 1:
![F_(31)=G(m_1.m_3)/(r_(31)^2)](https://img.qammunity.org/2020/formulas/physics/college/xqjmiiz5q03q9jygk7u94l3ued8ffctfg5.png)
![F_(31)=6.67* 10^(-11) * (6.7* 3.7)/(4.2^2)](https://img.qammunity.org/2020/formulas/physics/college/brkuiw8aytywpkf0et04vhfqe5gsaayd3d.png)
![F_(31)=9.37* 10^(-11)\ N](https://img.qammunity.org/2020/formulas/physics/college/yxjur52n5ikkiil99ykzlorh7hse48nzsu.png)
towards positive Y axis.
gravitational force on particle 3 due to particle 2:
![F_(32)=G(m_2.m_3)/(r_(21)^2)](https://img.qammunity.org/2020/formulas/physics/college/qbmrq9cf0lkm7f4njf3xdo4ihe0sbgouwr.png)
![F_(32)=6.67* 10^(-11) * (5.1* 3.7)/(2.8^2)](https://img.qammunity.org/2020/formulas/physics/college/d80gdfw00qanmqa6f73rsr1guqizyfop4b.png)
![F_(32)=16.05* 10^(-11)\ N](https://img.qammunity.org/2020/formulas/physics/college/k27z6s4g0j74bem3hnzskc46y4m8ur52fj.png)
towards positive X axis.
Now the net force
![F=\sqrt{F_(31)\ ^2+F_(32)\ ^2}](https://img.qammunity.org/2020/formulas/physics/college/r892jtpzup4kz8xzkuvf4hmm856l06a0d1.png)
![F=\sqrt{(10^(-11))^2(9.37^2+16.05^2)}](https://img.qammunity.org/2020/formulas/physics/college/tdwbia9t7796kbkx4nwsur18ezpffgby7q.png)
![F=18.58* 10^(-11)\ N](https://img.qammunity.org/2020/formulas/physics/college/v4saxd5wdjs74w7p2fp1x64x000um351at.png)
For angle in counterclockwise direction from the +x-axis
![tan\theta=(9.37* 10^(-11))/(16.05* 10^(-11))](https://img.qammunity.org/2020/formulas/physics/college/x47gdwecqajis2fd54eavv8eh5a1he5ipq.png)