An animal shelter spends $4.00 per day to care for each bird and $6.00 per day to care for each cat. Alexander noticed that the shelter spent $126.00 caring for birds and cats on Monday. Alexander found a record showing that there were a total of 26 birds and cats on Monday. How many birds were at the shelter on Monday?

15 birds

Step-by-step explanation:

In this case we can solve it using a 2x2 system of equations, like this:

let x: number of birds in the shelter

let y: number of cats in the shelter

So:

4 * x + 6 * y = 126

x + y = 26 = > x = 26 - y

Replacing, we are left with that:

4 * (26 - y) + 6 * y = 126

104 - 4 * y + 6 * y = 126

- 4 * y + 6 * y = 126 - 104

2 * y = 22

y = 2/22

y = 11

Now to calculate x:

x = 26 - 11

x = 15

Which means that there were 15 birds and 11 cats in the shelter.