Multiply the number in the tens place of the bottom
number by the number in ones place of the top number. So
multiply the 1 by the 5, which makes 5. Multiply the number in
the tens place of the bottom number by the number in tens
place of the top number. Multiply 1 by 2, which equals 2.
r is the x coordinate and s is the y coordinate. Positive slopes go from lower left to upper right, like going up stairs or up a hill. The line that goes through (r, s) that is positive is line B.
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