suppose that f : R-->R is strictly concave up, strictly increasing function with a zero t satisfying a<t< b

Which of the following are true

1.f(b)<0

2.f(b)=0

3.f(b)>0

4.f(a)<0

5.f(a)=0

6.f(a)>0

7.impossible to determine

can someone help me with this