Let's assume his previous score was x
we are given
John beat his previous high score in the favourite game by 28%
It means that
New score is 28 % greater than previous score
so,
New score = 28 % of previous score + previous score
now , we have assumed
previous score =x
so, we get
New score =

New score =

New score =

now, we are given
New high score is 288 points
so, we can plug it

now, we can solve for x

Divide both sides by 1.28

we get

so,
his previous score was 225 points..........Answer