Formula to use:
upper bound of speed = upper bound of distance/lower bound of time
Upper bound of distance = 146.25m
Lower bound of time = 6.5s
Upper bound of speed = 146.25/6.5
Preston answered it very well
To get the maximum value of the speed, you need the numerator (the distance to be large), while the denominator (time to be small)>
However in normal IGCSE question they will mention whether the time and distance are corrected to the nearest seconds or what not. Here we can only assume that it is corrected to the nearest smallest place value.