In a class there are 400 students. 250 of them studying Mathematics, 150 of them studying English, 100 of them studying Biology, 100 of them studying both Mathematics and English, 60 of them studying both Mathematics and Biology, 40 of them studying both English and Biology, 30 of them studying all Mathematics, English and Biology. Find
a) The number of students who are studying only Mathematics.
b) The number of students who are studying only English.
c) The number of students who are studying only Biology.
d) The number of students who are studying none of Mathematics, English and Biology.