To find the cost of the border around Gabrielle's garden, we can use the formula given:
\[ \text{Cost} = 1.50(2l + 2w) \]
where \( l \) is the length, and \( w \) is the width.
Plugging in the values \( l = 4 \) yards and \( w = 3 \) yards:
- Calculate the perimeter:
\[ 2l + 2w = 2(4) + 2(3) = 8 + 6 = 14 \text{ yards} \]
- Now, substitute this back into the cost formula:
\[ \text{Cost} = 1.50(14) \]
- Finally, calculate the total cost:
\[ \text{Cost} = 1.50 \times 14 = 21.00 \]
So, the total cost for the border around Gabrielle's garden is \($21.00\).