Answer:
[tex]9u-9t=18[/tex]
Step-by-step explanation:
The equation that completes the system is:
[tex]9u-9t=18[/tex]
First, we have to remember that tens value 10 units per digit, and units value one uni per digit. So, the number of the problem would be expressed like:
[tex]10t+u[/tex]
Now, the problem states that if the number is reversed its formed another number which is 18 units more than the original, that would be expressed like:
[tex]10u+t=10t+u+18[/tex]
Solving this relation, we have:
[tex]10u-u=10t-t+18\\9u=9t+18\\9u-9t=18[/tex]
Therefore, the expression that complete the system is the second equation.
