Let the total number of vote be x
Then the number of votes polled = x - 25% = x -0.25 = 0.75
So, number of votes polled for loosing candidate
= 40% of 0.75x = 0.40 * 0.75x
= 0.3x
So, number of votes polled for winning candidate
0.3x + 900
=> Number of votes polled
0.75x = 0.3x
( 0.3x + 900)
0.15 x = 900
x = 900 / 0.15
x = 6000