The answer is:
It takes Ella 3 seconds to do a push-up and 3 seconds to do a sit up.
<h2>Why?</h2>To find how many seconds Ella took to do a push-up and a sit-up we must write two equations using the given information.
Let be "x" the time needed to push-ups and "y" be the time needed to do sit-ups.
So, writing the equations we have:
First equation,
If she can do 13 push-ups and 7 sit-ups in 60 seconds, we have:
Second equation,
If she can do 13 push-ups and 19 sit-ups in 96 seconds, we have:
Now, creating a system of equations, and using the reduction method to solve it, we have:
Multiplying the first equation by -1, we have:
Then, substituting "y" into the first equation, we have:
Hence, we have that It takes Ella 3 seconds to do a push-up and 3 seconds to do a sit up.
Have a nice day!