$7.$ With a $2\mathrm{.}0$ cm diameter telescope, a man standing on the shore is just able to resolve two lights on a boat a certain distance away. The two lights each emit light of wavelength $440$ nm $.$ What diameter telescope would be necessary to just resolve the lights if instead they each emitted light of wavelength $650$ nm $?$

a$)3\mathrm{.}60$ cm

b$)3\mathrm{.}10$ cm

c$)3\mathrm{.}40$ cm

d$)3\mathrm{.}25$ cm

e$)2\mathrm{.}95$ cm