hey guys.... im new to this forum as well as to the Science field.. Please help me with this physics sum.....

Given that F=a t^(-1) + b r^2 ,where F denotes force & t, time the dimensions of a & b are respectively,

i) L T^(-2) & T^(-2)

ii) T & T^(-2)

iii) L T^(-1) & T^(-2)

iv) ML T^(-3) & ML T^(-4)

v) L^3 T^(-3) & M L^2 T^(-2)

Please tell me how to find the values of 2 unknown terms (a & b) in one equation.......

Thanks !