Answer:
![\huge{ \bold{ \boxed{ \text{4a + 6}}}}](https://img.qammunity.org/2021/formulas/mathematics/college/puu6xhs4s1a2ky1tzlhmw267px8udusfrt.png)
Explanation:
![\text{ (3a + 7) + (a - 1)}](https://img.qammunity.org/2021/formulas/mathematics/college/mvm0gedmf9e2g3n1kgq045umnu35i9xdvu.png)
In addition , sign of each term in the expression remains unchanged. So, Remove the unnecessary brackets.
![\text{⇢ \: 3a + 7 + a - 1}](https://img.qammunity.org/2021/formulas/mathematics/college/g295wxacu21hjh2nhdgnwuqj0p3c3xqq4b.png)
Combine like terms. Like terms are those which have the same base. Only coefficients of like terms can be added or subtracted.
![\text{⇢ \: 3a + a + 7 - 1}](https://img.qammunity.org/2021/formulas/mathematics/college/zpvgtnor9rn2dhwyc7aicih9y7wmhxu6k2.png)
![\text{⇢ \boxed{ \text{4a + 6}}}](https://img.qammunity.org/2021/formulas/mathematics/college/3zgnq73ntj8x75sknv5mbf56thmge8nglq.png)
And we're done! :D
Hope I helped!
Best regards! :D
~TheAnimeGirl