Step-by-step explanation:
3(x - 4y) - 2(y + 7x)
= 3x - 12y - 2y - 14x
= 3x -14x -12y -2y
= -11x -14y
4
Step-by-step explanation:
1. if the mass of coffee worth $10 is 'x', then its worth is 10x, and the worth of the mixture is 5(x+20);
2. using the previous item it is possible to write the next equation:
5(x+20)=4*20+10*x; ⇒ x=4.
3. the required mass is 4 pounds.