Sarah had to limit her fat intake to 25% of total calories if the fat intake is 550 calories what is the total number of calories she consumed for the day

We assume, that the number 550 is 100% - because it's the output value of the task.
2. We assume, that x is the value we are looking for.
3. If 550 is 100%, so we can write it down as 550=100%.
4. We know, that x is 25% of the output value, so we can write it down as x=25%.
5. Now we have two simple equations:
1) 550=100%
2) x=25%
where left sides of both of them have the same units, and both right sides have the same units, so we can do something like that:
550/x=100%/25%
6. Now we just have to solve the simple equation, and we will get the solution we are looking for.

7. Solution for what is 25% of 550

550/x=100/25
(550/x)*x=(100/25)*x - we multiply both sides of the equation by x
550=4*x - we divide both sides of the equation by (4) to get x
550/4=x
137.5=x
x=137.5

now we have:
25% of 550=137.5

Hope i can you!