\(F=\frac{T_{max}-T_{min}}{T_{min}}=\frac{T_{max}}{T_{min}}-1\)

\(\frac{T_{max}}{T_{min}}=F+1=\frac{4r^2}{(1-r^2)^2}+1=\frac{4(0.6)}{(1-0.6)^2}+1=16\)