Way to set a string value to a number value?

I making code that will add two numbers that are put into a TextBox's Text property and return an answer into another TextBox. The code works perfectly, but if I type in a string and click the CalculateButton, it will give this error in the output: Players.Green_Lime2.PlayerGui.ScreenGui.CalculateButton.LocalScript:15: attempt to perform arithmetic (add) on string

Is there any way to block the strings and only accept numbers? The LocalScript is inside the CalculateButton. Here's the code:

print("Ready for calculating")
while true do
    wait(0.1)

local player = game.Players.LocalPlayer
local character = player.Character
local playergui = game.Players.LocalPlayer.PlayerGui
local calculatebutton = playergui.ScreenGui.CalculateButton
local textbox1 = playergui.ScreenGui.TextBox1
local textbox2 = playergui.ScreenGui.TextBox2
local answerbox = playergui.ScreenGui.AnswerBox

    calculatebutton.Activated:Connect(function(activated)
        if activated then
            answerbox.Text = textbox1.Text + textbox2.Text
            end
        end)
    end