Note that 1lb=16oz and set up multiplication/division to cancel out units that you do not need for the final answer. (Units cancel just like numbers, this is fundamental to dimensional analysis)
64oz($1.50/16oz)=$6.00
the correct answer is your third choice.
4x = 7(x-3)
1. Distribute that multiplicand 7: 4x = 7x - 21
2. Group the x terms together: Subtract 4x from both sides: 0 = 3x - 21
3. Solve for x: Add 21 to both sides: 21 = 3x
4. Divide both sides by 3 to obtain x = 7 (answer)
