I'm going to do the calculus way because it's easier
max height,
take derititive of the equation
h'(t)=-9.8t+6
find what value of t makes it equal to 0
t=6/9.8
if we inputed it for t we get
h(6/9.8)=2.43673...
2.43673...>2.4 so we don't need to change anything