Let
x -----> number of students that preferred vanilla cupcakes
y ----> number of students that preferred chocolate
we know that
x+y=750 -----> equation A
and
2/5=x/y
x=(2/5)y ------> equation B
substitute equation B in equation A
(2/5)y+y=750
solve for y
(7/5)y=750
y=750*5/7
y=536
find the value of x
x=(2/5)(736)
x=214
therefore
the answer is 214 students preferred vanilla cupcakes