Try this option:
if x+y=-9 is I (one)
and x+2y=-25 is II (two), then
if II-I, then (x+2y)-(x+y)=-25+9 ⇔ y=-16.
When vinegar, an acid, is mixed with baking soda, a base, the reaction is similar to the reaction of Alka-Seltzer and water; a salt, water and carbon dioxide are produced.
