Elementary Geometry for College Students (6th Edition)

By expanding the brackets we have: $2x + 2\times 1= 30 -6x -6\times (-2)$ $2x +2 = 30 -6x +12 = 42 -6x$ We add $6x$ to both sides and in the meantime we subtract 2 from both sides: $2x + 6x = 42-2$ $8x = 40$ We divide both sides by 8: $x = 40\div 8 = 5$