To find out how many more pounds of coffee you need, you can subtract the amount of coffee already in your cart from the desired amount of 1 1/2 pounds.
First, convert the mixed number 1 1/2 into an improper fraction. To do this, multiply the whole number (1) by the denominator of the fraction (2), and add the result to the numerator (1). This gives us (1 * 2) + 1 = 3/2 pounds.
Next, subtract the amount of coffee in your cart (3/4 pound) from the desired amount (3/2 pounds).
3/2 pounds - 3/4 pound = 6/4 pounds - 3/4 pound = (6 - 3)/4 = 3/4 pound.
Therefore, you still need 3/4 pound of coffee.
In conclusion, you need an additional 3/4 pound of coffee to reach the desired amount of 1 1/2 pounds.