Hi Cee,
Let's set up a proportion.
126 90
---- = -----
x 100
where x is the calorie count of regular bread.
We use 90/100 for our proportion. The low calorie bread contains 10% fewer calories meaning it contains 90% of the calories of regular bread.
Now, cross multiply and solve for x
12600 = 90x
x = 140
Regular bread had 140 calories per serving.