Which expression represents 81 decreased by an unknown number

Ac contractor is building a new subdivision outside of the city. he has started work on the first street and is planning on the other streets to run in a direction parallel to the first. the second street will pass through (-2,4) find the equation of the location of the second street in standard form. a.2x+y=2 b. x-y=2 c.2x+y=2 d.x+y=2

Answers; a) 135 degree’s b) 30 degree’s c) 180 or 0 degree’s d) 90 degree’s

What are “like terms”? why can we only add like terms?