Answer: x = 13, y = 8
Explanation:
Since 10x-9 and 4x+7 are supplementary (equal to 180)
you set up this equation:
10x-9+4x+7=180
combine like terms
14x-2=180
simplify
14x=182
x=13
setup for y is easy since we now have x
12y+25+4x+7=180
substitute 13 for x
12y+25+4(13)+7=180
simplify
12y+25+52+7=180
simplify further
12y+84=180
simplify again
12y=96
finally, divide
y=8