Answer:
The one you have selected is right
Step-by-step explanation:
A constant speed is a number being added or subtracted at the same right. In this case its 50 each time
50+50= 100
100+50=150
etc
The 2nd one is being multiplied by 10 and the 3rd one is adding 100 which wouldnt be right since you started out with 50.
Hope this helps (:
