Ok! I'm here to help.
First, you're going to want to make variables. Go into the world's properties, and select create variable. Type the name "Distance" into name, and select number as the type. Repeat this process, except name it "Speed"
Next, drag the "Distance" variable into the event, end set it's value to anything. Go into the world's functions, and drag "Ask user for a string" into the number box. Click other, and type a question about the distance. Repeat this for the "Speed" variable.
Third, drag the variable "Distance" set it's value to itself, found under expressions. click on this reference, and select math. Click "Distance/", and select time under expressions.
Where you want it have the zombie say something. Under the world's functions, drag"What as a string" into the value. Drag distance into that. You're done!