how do you rearrange this equation

weight=T1sin57+[T1cos57/cos23.5]xsin23.5

when you're trying to isolate T1?????

That is the same as:

weight=T1sin57+[T1cos57xsin23.5]/cos23.5

so factor the T1 out:
weight=T1(sin57+[cos57xsin23.5]/cos23.5)

Then divide the weight by the whole expression next to the "T1":
T1=weight/(sin57+[cos57xsin23.5]/cos23.5)