I don't understand your comment "Partition 3 is where my /opt mounted"

These are what you have mounted which I would assume is all your mount points mounted:
Filesystem kbytes used avail capacity Mounted on
/dev/dsk/c0t0d0s0 2031101 1098483 871685 56% /
/dev/dsk/c0t0d0s5 95951 37884 48472 44% /var
/dev/dsk/c0t0d0s6 2031101 588630 1381538 30% /stg
/dev/dsk/c0t0d0s7 492422 14 443166 1% /export/home

No /opt in there. ? No /usr in there either - so you can take part of slice 3 and part of slice 4 and make them new sizes - in effect, make one of them the size you need - then dump /var into it (easy to say - little more work than that).

Perderabo's suggestion is the quickest and easiest.