We will assume complete dissociation.
Since we have the molarity of OH solution, we can calculate the p(OH) as follows:
p(OH) = -log(molarity of OH) = -log(7.5×10-3) = 2.1249
It is known that: p(H) + p(OH) = 14
Therefore, p(H) can be calculated as follows:
p(H) = 14 - p(OH) = 14 - 2.1249 = 11.875