Cross multiply.
75 / x = 25 / 35
25x = 35(75)
25x = 2625
/25 /25
x = 105
Therefore 105 students liked skating.
Proof:
105 + 35 = 140.
140 * 0.75 = 105
140 * 0.25 = 35
140 (total) split into quarters.
35 + 35 + 35 + 35 = 140
35 + 35 + 35 = 105 (3 quarters liked)
35 = 35 (1 quarter disliked)