ユーザーフォーム使ってTextBox1とTextBox2に数字いれてTextBox3に足し算の結果だすような基本をまず調べればあとは適当にぐぐりゃ分かるわな

計算途中も変数いちいち宣言して代入していくといいわ
自分で何やってんのか見失わないようにするため

Sub testttt()
Dim drawingX As Double: drawingX = 2
Dim drawingY As Double: drawingY = 2

Dim realX As Double: realX = 2.1
Dim realY As Double: realY = 2.1

Dim diffX As Double: diffX = realX - drawingX
Dim diffY As Double: diffY = realY - drawingY

Dim ResultPosition As Double: ResultPosition = Sqr(diffX * diffX + diffY * diffY) * 2

MsgBox ResultPosition

End Sub