X = pencils, y = pens
8x + 6y = 8.50
4x + 4y = 5.....multiply by -2
----------------
8x + 6y = 8.50
-8x - 8y = -10 (result of multiplying by -2)
-----------------add
-2y = - 1.50
y = -1.50 / -2
y = 0.75 <=== pens cost 0.75
4x + 4y = 5
4x + 4(0.75) = 5
4x + 3 = 5
4x = 5 - 3
4x = 2
x = 2/4
x = 0.50 <== pencils cost 0.50
The equation of g(x) is 
Explanation:
Given that the function f(x) is 
Also, given that the function g(x) is a vertical stretch of f(x) by a factor of 4.
We need to determine the equation of g(x)
<u>Equation of g(x):</u>
The vertical stretch of the function can be determined by multiplying the factor 4 with the function f(x).
Thus, we have,

Substituting the values,we have,

Simplifying the values, we get,

Hence, the equation of g(x) is 