Question 979850
let the letters B, S and F represent the random variable of how much money Bruce, Sarah and Frank have.
 
S=F+20          (equation 1)    
S=B-40          (equation 2)
B=2F+10         (equation 3)
 
substitute equation 1 into 2
 
F+20=B-40       (equation 4)
 
substitute equation 3 into 4 in order to get the equation in terms of F only
 
F+20=2F+10-40
F+20=2F-30
F=50
 
Sub the value of F=50 into equation 1 and 3 and you get: S=70 & B=110
 
Therefore, B=110, F=50, S=70