get an error if i press calculate-1 button without entries in the 4 Labels in Red

[jeff]

How do i change code in the userform so that i must have entries in the following Textboxs which are Red in colour on the Userform....i get an error if i hit the Calculate-1 button without entries in these 4 textbox`s
System Feed Flow
Feed Concentration
Outlet Concentration
CT Feed Flow

Also how do i make the results show as whole numbers?

Also can the colour of the numbers in the result box`s be Blue?

Still new to VBA code so i have i made this coding correct...it does work though

Best Regards

Jeff