Please Help Me Do This I cant understand it no matter how hard I try. (Problem in the image)

65 8 7 4 5 6 8 4 3 2 1 9 5 6 4 2 1 6 5 1 5 1 3 2 3 5 multiply the third number in the first row by the seventh number in the third row. add this result to the fifth number in the second row. add to this total ten times the fourth number in the third row. subtract the eighth number in the first row from the result.

Just tell me how to set up the equation.

In a class, there are 12 girls. if the ratio of boys to girls is 5: 4 how many boys are there in the class