we know that
A relationship between two variables, x, and y, represent a proportional variation if it can be expressed in the form
y=kx
where
k is the constant of proportionality
In this problem we have that
[tex]y=k\sqrt{x}[/tex]when y=29, x=100
step 1
find the value of k
substitute the given values in the expression above
[tex]\begin{gathered} 29=k\sqrt{100} \\ 29=10k \\ k=2.9 \end{gathered}[/tex]step 2
we have the equation
[tex]y=2.9\sqrt{x}[/tex]For x=123
substitute the value of x and solve for y
[tex]\begin{gathered} y=2.9\sqrt{123} \\ y=32.16 \end{gathered}[/tex]