Step-by-step explanation:
what's the question ? it does not say.
I assume it is "how many packages of what size were sold ?"
x = number of small packages
y = number of medium packages sold
z = number of large packages sold
x + y + z = 9
7x + 12y + 15z = 86
y = 3z
these are the 3 equations we get out of the question.
we put the third equation into the other two :
x + 3z + z = x + 4z = 9
7x + 12×3z + 15z = 7x + 36z + 15z = 7x + 51z = 86
it of this first equation we get
x = -4z + 9
and putting that into the other equation :
7×(-4z + 9) + 51z = 86
-28z + 63 + 51z = 86
23z = 23
z = 1
y = 3z = 3×1 = 3
x = -4z + 9 = -4×1 + 9 = -4 + 9 = 5
so, 5 small, 3 medium and 1 large packages were sold.
