Ineed to to have exactly 2,000 points, take also how would you know when to solve an equation algebraically? explain if you can.

Note: Based on the nature of your question I'm assuming you mean basic algebra. Algebra is a very broad field.

Basic algebra is essentially just the process of manipulating symbols which most commonly represent a currently unknown value. For example, a+5=10: the unknown value is a. You can find a by subtracting 5 from the left side of the '=' sign (which isolates the variable 'a') and subtracting 5 from the right side (which leaves you with 5) the equation you are left with is a=5, which you can plug in to your original equation 5+5=10. You need to solve a question algebraically anytime there are letters or variables by performing mathematical operations to both sides of the '=' symbol, so that it keeps the same value. If I answered your question poorly, please rephrase it so I can better understand.

the answer is 13 cm