AB = 3x + 4
BC = 7x + 9
AB + BC = AC
AC = 143
Let us add AB and BC then equate their sum by 143
[tex]AC=AB+BC=3x+4+7x+9=(3x+7x)+(4+9)[/tex]First, step add the like terms
[tex]AC=10x+13[/tex]Equate AC by its length 143
[tex]10x+13=143[/tex]Now we have an equation to solve it
To solve the equation let us move 13 from the left side to the right side by subtracting 13 from both sides
[tex]\begin{gathered} 10x+13-13=143-13 \\ 10x=130 \end{gathered}[/tex]To find x divide both sides by 10 to move 10 from the left side to the right side
[tex]\begin{gathered} \frac{10x}{10}=\frac{130}{10} \\ x=13 \end{gathered}[/tex]Now let us find AB and BC
Substitute x by 13 in each expression
AB = 3(13) + 4 = 39 + 4 = 43
BC = 7(13) + 9 = 91 + 9 = 100
The length of AB is 43 units
The length of BC is 100 units
