Answer:
14
Step-by-step explanation:
Let the number of white marbles be W and the number of red marbles be R, therefore, W + R = 25
and, W = 2R -8
Using first equation, R = 25 - W and putting it in second, we get,
W = 2(25 - W) - 8
W = 50 - 2W - 8
3W = 42
W = 14