Attaching short shirt sleeve to bottom of pant leg

I’m very new to sewing (have only machine hemmed a several pairs of pants new) but my buddy asked me to detach the sleeves of a heavy duty short sleeve shirt and reattach them to the bottoms of a pair of jeans (mainly to length them and add some pazazz). I’ve done my own research but nothing seems to fit or make sense. My experience is with little reference to any formal patterns or measurements, just eyeballing and fiddling around with things and then winging it. TIA! Also— i can add photos of materials at a later date if need to help explain situation