The system of equations becomes:
s + u = 28 This represent the number of candles sold
16s + 10u = 400 This represents the value of the candles sold
Just plug in -1 for x and u should get ur answer
The line passes through (2,-3) and (4,2).
Calculate the slope of the line.
m = (2+3)/(4-2) = 5/2
The equation of the line is therefore

Cross multiply.
2(y-2) = 5(x-4)
2y - 4 = 5x - 20
2y = 5x - 16
Rewrite as
5x - 2y = 16
Answer: C. 5x - 2y = 16