When will i know when to add or when to subract

You will know when to add or subtract because of keywords and symbols.

Step-by-step explanation:

Most addition and subtraction problems have keywords that tell you what operation to use. For example, so keywords that tell you that you have to add are altogether, sum, together, and a few other words. Some examples of subtraction problems are less than, and a bunch of other words.

Hope This Helps :)

let x be the money she spent so that she can earn the free t-shirt.

since, she already spent $112.49

⇒

also, as per the statement: jennifer must spend $250 or more in order to qualify for a free t-shirt at the store.

then,

we have an inequality i.,e

subtract 112.49 from both sides we get;

therefore, $137. 51 more money does jennifer need to spend so that she can earn the free t-shirt