First, we need to find the sum of all the numbers of the dice. The expression 3(1 + 2 + 3 + 4 + 5 + 6), or 3(21) does that for us. 3 × 21 = 63. So the sum of all of the numbers of the dice is 63. But we already know 7 of the numbers there: 2, 3, 1, 6, 5, 4, 5. In the expression 3(21), we counted these numbers as well. So now we can add these 7 numbers together then subtract them from 3(21), or 63. We can write the expression 3(21) - (2 + 3 + 1 + 6 + 5 + 4 + 5), or 3(21) - 26 = 63 - 26 = 37.
Lines are perpendicular if the slope of one is the negative reciprocal of the other. In this case the slopes are -8/3 and 8/3, so while negative they are not reciprocal. So no, the two lines intersect but are not perpendicular.
