y = her salary,
m = rate of commission,
x = amount of merchandise sold
b = monthly base pay
sets of data to calculate the formula
(500, 405) and (900, 489)
use the slope formula to find m:
(489 - 405) / (900 - 500)
m= 84 / 400 = 0.21 (21% commission)
find the base pay by substituting known values for x,y, and m, then solve for b:
405 = (0.21)(500) + b
405 = 105 + b
b = 300
now we know the equation for her salary is:
y = 0.21x + 300
To find the salary when she sells $1,700 worth of merchandise, put 1700 for x and solve for y:
y = 0.21(1700) + 300 = 657