An water well is to be drilled in the desert where the soil is either rock, clay or sand. The probability of rock P (R) = 0.53. The clay probability is P (C) = 0.21. The sand probability is P (S) = 0.26. It if it rock, a geological test gives a positive result with 35% accuracy. If it is clay, this test gives a positive result with 48% accuracy. The test gives a 75% accuracy for sand. Given the test is positive, what is the probability that the soil is rock, P (rock | positive)?