A store has x number of shirts. Each shirt was sold for $16, but the last dozen was sold on sale for $14 each. When all shirts were sold, the store gained $616. Find the number of shirts sold at the regular price.

28 shirts

Step-by-step explanation:

Let's see what we are given.

there are x amount of shirts ($616 total)

there are 12 in a dozen

the regular shirts are $16

the last 12 shirts are $14

Lets make an equation.

616= 14(12) + 16x

616=168+16x

448=16x

x=28

(Sorry if this explanation is bad)

Changing the equation into slope form: , where  is the slope [gradient] and  is the y-intercept.






The gradient is  and y-intercept is at 

Graphing using slope-intercept method:
a) The slope is a negative slope. The line will go 'down hill'
b) The line must pass the point (0, 490)
c) The line will intercept the x-axis at y = 0
    
    
    
    
    
    So, x-intercept is at (735, 0)

The graph of this function is shown below. The intercepts are labelled at:
y = 490
x = 735

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Next month's profit equation



Rewriting this into slope-equation form





The gradient, , equals to 
The y-intercept, , equals to 531

The equation still has the same gradient with last month's profit equation but different y-intercept. 

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A linear graph show points of (0, 300) and (450, 0)

We work out the slope: 


Y-intercept at x = 0, so it's at y = 300

Equation