ANSWER
As given in the question
use D for the number of doughnuts,
M for the number of muffins and B for the number of bagels.
The bakery makes three times as many doughnuts as bagels
equations becomes
D = 3B
bakery sells all 130 items in stock
equations becomes
D + B + M = 130
Bakery earn a total of $150
equations becomes
1.00D + 1.50M+ 1.20B = 150
On simplier terms
1D + 1.5M + 1.2B = 150
three equation are become in the form
D = 3B
D + B + M = 130
1D + 1.5M + 1.2B = 150
subract D + B + M = 130 equation from 1D + 1.5M + 1.2B = 150
1D -1D + 1.5M -M + 1.2B -1B = 150 -130
0.5M + 0.2B = 20
in simple form
5M + 2B = 200
Put D = 3B in the equation D + B + M = 130
we get
4B + M = 130
Now multiply 4B + M = 130 by 5 and subtracted from 5M + 2B = 200
5M - 5M + 2B - 20 B = 200 - 650
-18 B = - 450
B = 25
Put this value in the D = 3B
we get
D = 25× 3
= 75
Put the value of D and B in the equation D + B + M = 130 .
75 + 25 + M= 130
130 - 100 = M
M = 30
items are in stock at the bakery is doughnuts = 75 , muffins = 30 , bagels = 25.
Hence proved
