13,7-18,85

To calculate \( 13.7 - 18.85 \):

1. Align the numbers:

\[ \begin{array}{r} 13.70 \\ - 18.85 \\ \hline \end{array} \]

2. Proceed from right to left, borrowing if necessary:

• In the hundredths place: \( 0 - 5 \) requires borrowing. So, we take 1 from the tenths place (making it 6) and add 10 to the hundredths place, which becomes \( 10 - 5 = 5 \).
• In the tenths place: Now we have \( 6 - 8 \), which also requires borrowing. We take 1 from the units place (making it 12) and add 10 to the tenths place, turning it into \( 16 - 8 = 8 \).
• In the units place: \( 12 - 18 \) requires borrowing as well, so \( 12 - 18 = -6 \).

Putting this together, the overall calculation gives us:

\[ 13.70 - 18.85 = -5.15 \]

So, the result is:

\[ \boxed{-5.15} \]