The first number is coefficient for i, and the second number is coeff. for j
=>
<0,-8> is the same as 0i-8j, or simply 8j
I believe you combine the first and last terms first because they have the same denominator
175 students walk to school. 7+5=12 and 420 divided by 12 is 35. I checked how I did it was correct because of 5*35+7*35=420. Then I found the product of 5*35 which is 175.