Answer:
[tex]\boxed{\bold{a=33}}[/tex]
Step-by-step explanation:
Note: [tex]\bold{":" \ Means \ The \ Mean \ Of \ Two \ Numbers}[/tex]
Mean Of 9 & 3: 3
Rewrite Equation
[tex]\bold{48\cdot 3\:-\:a\:+\:\left(3\:+\:15\right)=\:129}[/tex]
Remove Parenthesis: (a) = a
[tex]\bold{48\cdot \:3-a+3+15=129}[/tex]
Multiply Numbers: [tex]\bold{48\cdot \:3=144}[/tex]
[tex]\bold{144-a+3+15=129}[/tex]
Group Like Terms
[tex]\bold{-a+144+3+15=129}[/tex]
Add The Numbers: [tex]\bold{144+3+15=162}[/tex]
[tex]\bold{-a+162=129}[/tex]
Subtract 162 From Both Sides
[tex]\bold{-a+162-162=129-162}[/tex]
Simplify
[tex]\bold{-a=-33}[/tex]
Divide Both Sides By -1
[tex]\bold{\frac{-a}{-1}=\frac{-33}{-1}}[/tex]
Simplify
[tex]\bold{a=33}[/tex]
