You cannot test everything at once. Choose one variable to change, then decide what you will hold constant so the comparison is fair.
Real braking tests do not give the exact same number twice. How many runs do you need before you would trust the result?
Before any data appears, draw the shape you expect. Use your finger or mouse and draw all the way across. You are committing to a claim — it is fine to be wrong, that is the useful part.
Each run is a separate braking test at the settings you chose. Watch your prediction line as the measurements land on top of it.
Write up what you found. Your evidence is the table above — use the actual numbers.
Answer your question in one sentence. What effect did your variable have?
Quote at least two measurements from your data, including units. Compare them.
Connect it to forces and motion. What is the unbalanced force here, and why does changing your variable change how far the vehicle travels before it stops?
Speed and surface change the forces involved. Load changes the mass. Investigate all three before you decide what controls stopping distance.