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Could someone help me with these math problems? I can't figure them out. Solve the linear equation;
x+2y=15
y=-2x+0 9x-12y=-3
-12x+16y=4? 7^(x+1) + 7^x + 7^(x-1) = 399, what is x? How many edges in a circle? Find the complement of the angle 3pi/7. Please show steps!? 0.8 litres water is how many cups?