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**Mist** A particle Pis moving on the x-axis with constant decleration 4ms-2. At time t=0, P passes through the origin O with velocity 14ms-1 in the positive direction. The point A lies on the axis and OA=22.5. Find a) the differance between the times when P passes through A, b)The total distance travelled by P during the intervals between the lines.

I was able to answer the first half of the question but I got stuck in the middle of it. I reached till 0=-4t^2+28t-50. I used the quadratic formula but I got the wrong answer and I can't figure a way to factorise it.

Any help?