Question 75618
1) The solution to {{{4x = 10-cy}}} is (5, -2).
What is the value of c?
Since you have been given the solution of (5, -2) you can substitute x = 5 and y = -2 into the given equation and solve for c.  
{{{4(5) = 10 - c(-2)}}} Simplify.
{{{20 = 10 + 2c}}} Subtract 10 from both sides of the equation.
{{{10 = 2c}}}  Finally, divide both sides by 2.
{{{c = 5}}}

2) If g(x) = 2x+3 find g(9)  Substitute 9 for x in the function.
g(9) = 2(9)+3
g(9) = 18+3
g(9) = 21

3)If {{{h(x) = x/2 - 7}}}, find h(4)  Substitute 4 for x in the function.
{{{h(4) = 4/2 - 7}}}
{{{h(4) = 2-7}}}
{{{h(4) = -5}}}

If y varies directly as x, you can write: y = kx where k is the constant of proportionality.  To find the value of k, susbstitute the given x = 3/2 and y = 1/4
{{{1/4 = k(3/2)}}} Multiply both sides by {{{2/3}}}
{{{k = 1/6}}}
Now you have:
{{{y = (1/6)x}}} Substitute x = 54.
{{{y = (1/6)(54)}}}
{{{y = 9}}}