Given: 30%×(x+y)=40%×(x−y) Concept: Calculate the value of x with respect to y, and then substitute the vale un the question to find the answer. Calculation: ∵30%×(x+y)=40%×(x−y) ⇒3(x+y)=4(x−y) ⇒3x+3y=4x−4y ⇒3y+4y=4x−3x ⇒7y=x ∴(3x−y)/(x+y) ⇒[(3×7y)−y]/(7y+y) ⇒(21y−y)/8y ⇒20y/8y ⇒