let t = Tom's age 
let g = Gary's age 
let r = Reb's age 
let s = Sam's age 
: 
tom is four less than twice gary's age. 
t = 2g - 4 
: 
Gary's age
2g - 4 = t 
2g = t + 4 
g = t+4 over 2
: 
rebecca is the youngest and she is two less than half gary's age after it was increased by three. 
r = .5(g+3) -2 
: 
sam's age is the ratio of seven more than gary's age to eight less than gary's age. 
s= (g+7) over (g-8)