equal fraction concept
step 1: find equal fractions
"After she sold 1/2 of the cookies and 1/4 of the muffins, she had an equal number of cookies and muffins left."
this means, the cookies and muffins left are equal
cookies left = muffins left
cookies left → 1/2 muffins left → 1 - 1/4 = 3/4
step 2: make numerators the same
1/2 cookies = 3/4 muffins 3/6 cookies = 3/4 muffins
step 3: convert to units
total cookies → 6u cookies left → 3u cookies sold → 3u
total muffins → 4u muffins left → 3u muffins sold → 4u - 3u = 1u
total → 1200 total (units) → 6u + 4u = 10u
10u → 1200
1u (muffins sold) → 1200 ÷ 10 = 120
3u (cookies sold) → 3 x 120 = 360
total raised → 360 x $2.10 + 120 x $3.50 = $1176