Private Sub btnCompute$\_$Click$(...)$ Handles btnCompute.Click

Dim shapeNum As Integer

Dim radius, length, height, width As Double

'Input choice of shape and its dimensions

$\text{'}1.$ Circle $2.$ Parallelogram $3.$ Kite

shapeNum $=$ CInt$($mtbSelection$.$Text$)$

'Mask is $0$

Select Case shapeNum

Case $1$

radius $=$ CDbl$($InputBox$("$Input the radius of the circle: $"))$

txtArea.Text $=$ CStr$(3\mathrm{.}141593*$ radius $^2)$

Case $2$

length $=$ CDbl$($InputBox$("$Input the length of the parallelogram: $"))$

height $=$ CDbl$($InputBox$("$Input the height of the parallelogram: $"))$

txtArea.Text $=$ CStr$($length $*$ height$)$

Case $3$

length $=$ CDbl$($InputBox$("$Input the length of the kite: $"))$

width $=$ CDbl$($InputBox$("$Input the width of the kite: $"))$

txtArea.Text $=$ CStr$(($length $*$ width$)/2)$

Case Else

MessageBox.Show$("$Your choice is not valid.", "Try Again."$)$

mtbSelection.Clear$()$

End Select

mtbSelection.Focus$()$

End Sub. Explain in detail how this works