book Maths Puzzle Numerical Ability

If the system 2x-5y=1 and -3x+7y=-3 is to be solved by elimination of x, and the first equation is multiplied by 3, then by which number should the second equation be multiplied?
*I think that the answer is 2.Is this correct?

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book Other Question

A and B walk up an excavator. The elevator (moving stairs) moves at a constant speed. A takes six steps for every 4 steps of B . A gets to the top of the elevator after having taken 50 steps. While B takes 40 steps to reach the top (because pace of B is slower than A). Now suppose elevator is turned off .how many stairs will they have to climb to get to the top. The process to solving the patial proportion