John and paul spent $45 altogether. john and henty spent $65 altogether. if henry spent 3 times as much as paul, how much did john spend?

Lets x is the amount of money Paul spent
y  is the amount of money John spent
Henry spent 3 times as much as paul = 3x

so

John and paul spent $45 altogether: x + y = 45
 john and henty spent $65 altogether: 3x+y = 65

solve the equations

3x+y = 65
 x + y = 45
subtract
2x = 20
x = 10 

 x + y = 45
y = 45 - x
y = 45 - 10
y = 35

3x = 3(10) = 30

so 
Paul  spent $10 (x)
John spent $ 35 (y)
Henry spent $30 (3x)

John spent $ 35 

double check:

$ 35 + $ 10 = $45 (John and Paul spent $45 altogether)
$ 35 + $30 = $65 ( John and Henry spent $65 altogether)