let the number of reds be r, let the number of whites be w
r + w = 12 and r<w and both r and w must be whole numbers
let the price of a white be x cents, then the price of a red is x+3 cents.
clearly x also must be a whole number.
then r(x+3) + wx = 129
rx + 3r + wx = 129
x(r+w) = 129-3r, but r = 12-w
x(12-w+w) = 129-3r
x = (129-3r)/12
we stated that x had to be a whole number, and the only choices for r are:
the only value which gives a whole number for x is when r = 3
then w = 9, and x = 10
so a white costs 10 cents, and a red costs 13 cents.
but 3(10) + 9(13) is not equal to 129
so your data is inconsistent and there is no solution to your question.
Ignore the last two lines of my previous posts, I subbed in the price for the wrong colours.
Obviously 3(13) + 9(10) = 129
So there were 3 reds and 9 whites.