A (-4, 3)
B(-4, 1)
C(-2, 1)
When you reflect about the y-axis, the coordinate becomes (-x, y)
A(-4, 3) ⇒ A' ( 4, 3)
B(-4, 1) ⇒ B' (4, 1)
C(-2, 1) ⇒ C' ( 2, 1)
To find the length of B'C', we will use the distance formula
![|d|=\sqrt[]{(x_2-x_1)^2+(y_2-y_1)^2}](https://img.qammunity.org/2023/formulas/mathematics/college/6y55gyuxr0zmmcm1w6cs5srcfzsrudsayf.png)
x₁=4 y₁= 1 x₂=2 y₂=1
substitute the coordinates in the above
![|d|=\sqrt[]{(2-4)^2+(1-1)^2}](https://img.qammunity.org/2023/formulas/mathematics/college/glsseexwgm2mm813b7rhn5n7woz7q75arr.png)
![=\sqrt[]{(-2)^2+0}](https://img.qammunity.org/2023/formulas/mathematics/college/z83ycpwpmg1zsimb91lxecjt6mroppegvy.png)
![=\sqrt[]{4}](https://img.qammunity.org/2023/formulas/mathematics/college/4yt8b6irc8ojpi5rys9em8detgnyspvi60.png)

Hence, the length is 2