A biased spinner has the numbers 1 2 3 4 what is the probability of getting a 4?

Without information about the bias, there can be no possible answer. You cannot even say that the probability of 4 is not 0.25 since suppose the spinner has the following probabilities:

Pr(1) = 0.1 Pr(2) = 0.4 Pr(3) = 0.25 Pr(4) = 0.25

is clearly biased - in favour of 2, but the probability of 4 is not affected by the bias.