To find the cost for a garden that has a length of 4 yards and a width of 3 yards, we substitute l = 4 and w = 3 into the formula 1.50(2l+2w):
Cost = 1.50(2 * 4 + 2 * 3)
= 1.50(8 + 6)
= 1.50(14)
= $21.00
Therefore, the cost for a garden that has a length of 4 yards and a width of 3 yards is $21.00.