If a vehicle travles with a constant acceleration of 3km/hr for 5 hours, what was its initial velocity if the final velocity was 100km/hr?

Can you please show me how to work this out in math terms.Can you explain it to me.
thank you so much.

Do read the earlier two first.

At the end of hour five, which we'll call t5,

speed @t5 = 100 km/h

It's been accelerating at 3km/h, so at 4 hours

speed @t4 = 100 - 3 = 97 km/s

and at 3 hours

speed @t3 = 97 - 3 = 94 km/s

You can work it back from there.