Question

5x=1/2y-1, find value of X; 1/4y=10x-1, find value of Y (use substitution)

Answer 1

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

Answer 2

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