There are some online tools that will help you. 1lb of DME in 1g of water contributes about 46 gravity points (1.046).
1.5 gallons of 1.140 wort should bring you up to 5.5 gallons of 1.061 wort assuming you started at 4 gallons of 1.032
Something is always fermenting....
"It's Bahl Hornin'"
Kegged: Bourbon Barrel Imperial Stout
On Deck: German Lager