To find out how much Linda will spend on 35 packs of multi-colored paper, we need to multiply the cost of one pack by the number of packs she is purchasing.
The cost of one pack is $3.99. Therefore, the total cost for 35 packs can be calculated as follows:
\[ \text{Total Cost} = \text{Cost per Pack} \times \text{Number of Packs} \]
\[ \text{Total Cost} = 3.99 \times 35 \]
Now we can do the multiplication:
\[ 3.99 \times 35 = 139.65 \]
Thus, Linda will spend $139.65 on 35 packs of paper.