Solve. Four times a number is equal to the number increased by 21. Find the number.
The number is

Let x equal the number

 Tip: Go step-by-step

4 times a number is translated to... 4x

Is equal to means =

to the number increased by 21 is... x+21

Your equation is: 4x=x+21

Subtract x from both sides

3x=21

Divide three from both sides

x=7

Check!

4(7) = 7+21

28=28!

Correct!

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explanation:

previous steps have made pa≅ pb ≅ st ≅ su. setting the compass width to ab allows you to make tu the same length. then δstu ≅ δpab by the sss congruence postulate, and ∠p ≅ ∠s by the reason cpctc.