Hi,

I bought a used '99 Trek 240 bicycle for my son and I'm trying to
modernize it. It has an old shimano sis derailer, a 7 speed 12-28T
cassete and 24-34-42T crank set.

I would like to replace the shifters and the derailer and I rushed to
buy the stuff without consulting first. I ordered two different
derailers just in case .
Here is what I ordered from Amazon (haven't received any of it yet):

SRAM MRX Comp Grip Shifter, 7 Speed, Set
Shimano RD-CT95 Altus Rear Derailleur, 7/8 Speed, Smart Cage, Black
Shimano Alivio Rear Derailleur, 8 speed

Can someone say if the shifter will work with any of the two
derailers?

Thanks,
Slava.