exam Maths Puzzle Numerical Ability

I need help using the echelon method to solve each of two equations in two unknowns.

2x + 7y = -8
-2x + 3y = -12

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exam Other Question

5m-2(m-5)=17 if someone wanted an average grade of 90 and they base the grade on 4 tests and the first 3 scores were 84 93 and 88 what would the last test score grade have to be to get a total average of 90?
85
88
92
or
95