Answer:
System of Equations
3x + 1.5y = 18..... Equation 1
x = 3y ... Equation 2
This is not viable 
Explanation:
Let us represent
Number of roses = x
Number of camations = y
Juan is buying flowers for his mother. He has $18 to spend and sees that roses are $3 each and camations are $1.50 each. 
$3 × x + $1.50 × y = $18
3x + 1.5y = 18..... Equation 1
He wants to buy 3 times as many camations as roses 
y = 3x.... Equation 2
Therefore: 
System of Equations
3x + 1.5y = 18..... Equation 1
x = 3y ... Equation 2
This is not viable