How many protons does it has if Phosphorus has an atomic mass of 30 and 15 neutrons?

The correct answer is 15.
If Phosphorous has an atomic mass of 30 and 15 neutrons the proton number is most likely 15.

The mass number of of atoms in an element is equal to the sum total of the number of neutrons and protons. Since we have the atomic mass and the number of neutrons, it is easy to determine the number of protons
Atomic mass = number of proton + number of neutrons
Let X be number of protons
30 = X + 15
X = 30 – 15
= 15
Therefore the number of proton is 15.