Solution
Let x the number of cookies and y the number of brownies
From the conditions given we can create the following equations:
6x + 12y= 744 (1)
x +y = 80 (2)
If we solve x from the equation (2) we got:
x= 80-y
And replacing into the equation (1) we got:
6(80-y) +12y = 744
And solving we got:
480 - 6y +12 y= 744
6y = 744-480= 264
6y = 264
y= 264/6= 44
And solving for x we got:
x= 80- 44= 36
Then the number of cookies needs to be at least 36 and the number of brownies needs to be at least 44