Answer :

To find the sum of the terms [tex]\(-3 y \sqrt{13}\)[/tex] and [tex]\(4 y \sqrt{13}\)[/tex], follow these steps:

1. Identify the like terms:
- Both terms involve the variable [tex]\(y\)[/tex] and the irrational number [tex]\(\sqrt{13}\)[/tex].

2. Combine the coefficients of [tex]\(\sqrt{13}\)[/tex]:
- The coefficient of [tex]\(\sqrt{13}\)[/tex] in the first term is [tex]\(-3\)[/tex].
- The coefficient of [tex]\(\sqrt{13}\)[/tex] in the second term is [tex]\(4\)[/tex].

3. Add the coefficients:
[tex]\[ -3 + 4 = 1 \][/tex]

4. Multiply the resultant coefficient by [tex]\(\sqrt{13}\)[/tex]:
[tex]\[ 1 \cdot \sqrt{13} = \sqrt{13} \][/tex]

Thus, the sum of [tex]\(-3 y \sqrt{13}\)[/tex] and [tex]\(4 y \sqrt{13}\)[/tex] is:
[tex]\[ \sqrt{13} \][/tex]

The numerical value of [tex]\(\sqrt{13}\)[/tex] is approximately:
[tex]\[ \sqrt{13} \approx 3.605551275463989 \][/tex]

So, the combined expression simplifies to:
[tex]\[ y \cdot 3.605551275463989 \][/tex]

Therefore, the sum is:
[tex]\[ y \sqrt{13} \approx y \cdot 3.605551275463989 \][/tex]