Probability of getting 0 blue disks p(0) = 3/4 * 3/4 * 3/4 * 3/4 = 81/256
Probability of getting 4 blue disks p(4) = 1/4 * 1/4 * 1/4 * 1/4 = 1/256

Probability of getting 1,2, or 3 blue disks p(1, 2, 3) = 1 - 81/256 - 1/256 = 174/256 = 87/128 (C).