Summing random numbers C#?

Question

C++ / C#

Need help urgently! How to add values ​​from textbox to label every time the button is clicked (that is, when the button is pressed, a random value from 1 to 100 is displayed in the textbox, and then duplicated in the label immediately, and with the next click a new random value is added) I will be grateful for the
help 1+75+3 = 1753
Needed: 1+75+3= 79