Answer:
![\boxed{50 }](https://img.qammunity.org/2023/formulas/mathematics/high-school/7alqyv24ch7pzcu4emur8efrear7ahq96f.png)
Explanation:
What is a Triangle?
A triangle is the simplest polygon. It is a two-dimensional shape with three straight sides forming an interior, closed space. It has three interior angles.
1. Subtract the two known angles from 180°
2. Plug the two angles into the formula and use algebra:
![\boxed{a+b+c=180}](https://img.qammunity.org/2023/formulas/mathematics/high-school/upmvzeux76exkrjrmgm2tuqckwah3zvbho.png)
3. Subtract
![\boxed{180-40 =140}](https://img.qammunity.org/2023/formulas/mathematics/high-school/buh5dcvt7obbzo2esgx8zkw17ww2qe4qnj.png)
![\boxed{140-90=50}](https://img.qammunity.org/2023/formulas/mathematics/high-school/fsxt13jljtedpmgdjsba9o7hbm6uvg3419.png)
![c=50](https://img.qammunity.org/2023/formulas/mathematics/high-school/8m9c3pf7jnrs9wrtf845sy7srhg2w6qnk9.png)
Therefore, The Answer is 50
![-TheAnimeGirl-](https://img.qammunity.org/2023/formulas/mathematics/high-school/c7tuy2bzx6pnwxr4wn2y3eaw2afr0lwb28.png)