if a car has an initial velocity of 103m/s and acclerates at 1m/s for 3 seconds what will its final velocity be

looks pretty straighforward without any Physics or Calculus

at time = 0, v = 103
at time = 1, v = 104
at time = 2, v = 105
at time = 3, v = 106

btw, your acceleration should have been 1m/s2