I WILL MARK BRAINEST!! number 4 please. i know the answer to the question it’s just that i don’t know how they got that answer please help me i’m literally desperate at this point thank you so much

Answer:
2a+2b+4
Step-by-step explanation:
(2a+2b+4)+(3a+8)+(5a+b)=10a+3b+12
Answer:
The perimeter of the triangle is [tex]10a + 3b + 12[/tex], while the two sides is [tex]3a + 8[/tex] and [tex]5a + b[/tex]. To find the missing side, subtract the two known sides from the known perimeter.
[tex](10a + 3b + 12) - (3a + 8) - (5a+b) = 2a+2b+4[/tex]
If we simplify this expression by taking out a factor of [tex]2[/tex], the final answer is: [tex]2a + 2b + 4 = 2(a + b + 2)[/tex].
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Step-by-step explanation:
See top.