2x decreased by 15 is equal to -27 The phrase decreased by 15 means we subtract 15 from 2x: 2x - 15 The phrase is equal to means an equation, so we set 2x - 15 equal to -27 2x - 15 = -27 <-- This is our algebraic expression To solve this, type 2x - 15 = -27 into the search engine.