"A number" is unknown so just create a variable in this case I made it "n."
We know that sum means to add so add the variable n and 7 then going back up the beginning we see it says twice so we take that sum and times is by two and I'm using parentheses to show this. The next part of the problem says "Is" and that's an indication of an equal sign. We'll then put the equal sign after the problem we just filled out and finish off the equation with 3 times the number meaning we'll put the 3 and next to each other as another way of multiplying.
<span>Letisha will have earned however much money she began with plus 1.5 percent. This can be found by taking the initial principal on January 1 of the previous year, multiplying it by 0.015, and adding the result to the previous balance to get the end-of-year total.</span>