Part A) Start at 0 on the number line. Count out 7 spaces (each space is 0.25 units wide) so you'll end up at 1.75 which is the total cost. The 7 spaces refer to the number of postcards purchased.
Part B) Multiply 0.25 by 7 and you should get 1.75; alternatively, you can multiply 25 by 7 to get 175, then move the decimal point 2 spots to the left to get 175 ---> 1.75
