The number of green balls is g. The number of red balls is 3 more than the number of green balls, and the number of blue balls is 7 more that the number of green balls. If the number of blue balls is 18, how many green balls are there?
Just translate the English to Math, after all, Math is just a language.
let the number of green balls be g , as suggested
"The number of red balls is 3 more than the number of green balls" ---> reds = g+3
"the number of blue balls is 7 more that the number of green balls" --> blue = g + 7
"the number of blue balls is 18" ---> g+7 = 18
g = 11
There are 11 greens
(Where do the red balls come in ??)