These questions are classic. They are a variant on the Two Cars Algebra problem. Just remember this formula: Distance = Velocity * Time Step 1) Plug in the numbers and put an "N" for your unknown variable: 900 = N * 16 Step 2) Do the easy math (PEMDAS) first: 900 = 16N Step 3) Solve for "N" by dividing both sides by 16: 900/16 = 16N/16 Step 4) Solved! Your answer should have been 56.25 = N Now we have the hidden number of 56.25. That is the velocity. Let's just use the same algebra equation again (Distance = Velocity * Time), except that now Time is the unknown variable: 400 = 56.25 * N 2) 400 = 56.25N 3) 400/56.25 = 56.25N/56.25 4) You can finish this one yourself. Here is a hint: Don't be frightened by a repeating decimal! Whether you use a vinculum or round up/down is up to your teacher. You could use a fraction but the units would not match, thus making it incorrect. I hope this was of help to you! If anybody has an easier way or any corrections, please feel free to post because I enjoy learning as well.