cant figure out

Let L   be the original length

Then

L (1.18)   = 25       divide both sides by 1.18

L = about 21.18644 cm

Check that     [  25 - 21.18644] / 21.18644   =  about 18%

Hint:  " of  " means multiply

18% of something = 25, so 18% * something = 25

We can say 18% * x = 25 to algebraically solve for an unknown.

18% = 0.18 because 0.18 * 100% = 18%

0.18x = 25, isolate the variable, you get x = 25 /0.18 = 138 8/9 or 138.889 ...

Hope this helps!

PS - this a thorough way to do this. There are quicker ways to get the answer, but this will do for now.

Let n be the number,

.18n=15 divide both sides by .18

n=15/.18

n=83 1/3

 Ooops!. My mistake. Took as 15 instead of 25                                                  Let n be the number,

.18n=25 divide both sides by .18

n=25/.18

n=138 8/9

maybe i described this poorly. 
A spring is stretched to 25cm. The spring is stretched 18% of its origional length. How long is the spring originally.

the issue is 

25/18 is 4.5 gives you 20.5 

but a 18% increase on 20.5 isnt 25

i go tthe answer right through just throwing numbers in but i wasnt ot know how to do it proper