Question 147025
Let x=Rosa's age
Then x+7=Marcos's age

Now we are told that:

x+x+7+1=3x collect like terms

2x+8=3x subtract 2x from each side
2x-2x+8=3x-2x collect like terms
x=8-------------------------Rosa's age
x+7=8+7=15 --------------Marcos's age

CK
8+15+1=3*8
24=24

Hope this helps---ptaylor