1. (x+3y)-((5y-6x)+7)-(9x+8y-12)
х+3у-5у+6х-7-9х-8у+12=х+6х-9х+3у-5у-8у=-2х-10у=-2(х+5у)
2. -(7p-8q)+(-9p-(4q+9))-(9q-(8+14p))-(5p-11q)=-7p+8q-9p-4q-9-9q+8+14p-5p+11q=-7p-9p+14p-5p+8q-4q-9q+11q+8-9=7p+6q-1
3.4s+2(3t-(3r-6s))-(5s-3(s-4(t-2r)))+2(4t+2r-2(3t+5s))=4s+6t-6r+12s-5s+3s-12t+24r+8t+4r-12t-20s
=-6s-10t+22r=-2(3s+5t-11r)