Instead, let's try working this together. By participating in the process, you will learn, "hands on", how to do this (and thus come to understand all the worked examples you've looked at) and, by reviewing your work and reasoning, we'll be able to "see" where you're actually needing help. So:
a variable to stand for one of the types of stamps. Let's say we pick "f" to stand for "one first-ounce stamp".
ii) Since she bought 45 in total, and "f" of them were first-ounce stamps, how many were left to be the "additional ounce" stamps? Create an expression, in terms of the variable in (i), for the number of additional-ounce stamps.
iii) The value of one first-ounce stamp is (39)(1) = 39 cents. The value of two is (39)(2) = 78 cents. Create an expression for the value of "f" first-ounce stamps.
iv) Using reasoning similar to that in (iii), create an expression for the value of the additional-ounce stamps.
v) Since the total value (in cents) is given as being 1500, and since this total is the sum of the values of the two types of stamps, add the two "value" expressions and set the sum equal to the given total.
vi) Solve the linear equation for the value of the variable.
vii) Back-solve to find the requested values.
If you get stuck, please reply showing how far you have gotten. Thank you!