$(2).$ If the optical signal power at the transmitter is $+7$ dBm $,$ estimate the optical signal to noise ratio $($OSNR$)($in dB$)$ after the first amplifier.

$($a$)39$ dB

$($b$)43\mathrm{.}8$ dB

$($c$)40\mathrm{.}2$ dB

$($d$)42$ dB

$(3).$ Estimate the OSNR $($in dB$)$ after the last amplifier.

$($a$)29\mathrm{.}8$ dB

$($b$)31\mathrm{.}2$ dB

$($c$)34\mathrm{.}2$ dB

$($d$)32\mathrm{.}4$ dB