What is the solution of (3(x+y)=57) and (4(x-y)=28)?

Correct answer: \((x,y)=(13,6)\)

Dividing the first equation by 3 gives \(x+y=19\), and dividing the second equation by 4 gives \(x-y=7\). Adding these equations gives \(2x=26\), so \(x=13\). Substituting \(x=13\) into \(x+y=19\) gives \(y=6\). Hence, the solution is \((x,y)=(13,6)\). In option A, \(x+y\) is not 19. Exam tip: First simplify equations by dividing out common coefficients, then use addition or subtraction to eliminate a variable.