The 5 is the 100,000 column, the 1 is the 10,000 column, the 3 is the 1,000 column, the 4 is the 100 column, the 2 is the 10 column and the 8 is the 1 column. Look at the number to the right of the number that you are rounding to. If the number to the right (In this case 4) is 5 or more, our number 3 will be rounded up to a 4. But of that number to the right is 4 or less, it stays the same.
The slope of line T is -1/5, because perpendicular lines have opposite reciprocal slopes, meaning the opposite sign (positive or negative) and flipped (whole number becomes a fraction).
