book Maths Puzzle Numerical Ability

I am very confused as to how to Solve each system by the additional method. Can someone help me understand this and solve it please?

17.) x + y = 48
12x + 14y = 628

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book Other Question

The earth weighs 5.974E21 metric tons and the sun is 1.99E27 metric tons how much more does the sun weigh in metrix tons. The answer should have atleast 4 digits. Can the solution set of the compound inequality x < -3 0r x > 5 be expressed as -3 > X > 5? Please explain.