How would I write f(x) = -4(x-2)+ 7 in standard form

Can someone explain the elimination method to me for this problem?

You were told that the amount of time lapsed between consecutive trades on the new york stock exchange followed a normal distribution with a mean of 15 seconds. you were also told that the probability that the time lapsed between two consecutive trades to fall between 16 to 17 seconds was 13%. the probability that the time lapsed between two consecutive trades would fall below 13 seconds was 7%. what is the probability that the time lapsed between two consecutive trades will be between 14 and 15 seconds?

Which equation results from adding the equations in this system? x+6y=9 and -x+2y=-15