Algebra
posted by Linda .
5x=1/2y1, find value of X; 1/4y=10x1, find value of Y (use substitution)

I assume you mean:
5 x = (1/2) y  1
(1/4) y = 10 x  1
and we are to solve the two equations simultaneously using substitution and get for x first
so solve the first for x as a function of y
x = (1/10) y  1/5
use that x in the second equation to get y
(1/4) y = 10 [ (1/10)y 1/5 ]  1
y = 4 y  8  4
3 y = 12
y = 4
Now use that value of y to get x
5 x = (1/2) 4  1
x = 1/5 
i need help in finding this answer
find the value of r so that the line through (8,R) and (4,5) has a slope of negative