To solve this problem we need to use the emf equation, that is,
[tex]E=m\frac{dI}{dT}[/tex]
Where E is the induced emf
I the current in the first coil
M the mutual inductance
Solving for a)
[tex]M=\frac{E}{\frac{dI}{dT}}\\M=\frac{1.6*10^{-3}}{0.245}=6.53*10^{-3}H[/tex]
Solving for b) we need the FLux through each turn, that is
[tex]\Phi=\frac{MI}{N}[/tex]
Where N is the number of turns in the second coil
[tex]\Phi=\frac{6.53*10^{-3}*1.25}{22}=3.71*10^{-4}Wb[/tex]