Looks like you did most of it.
The next step would be setting them equal to 105, like the problem suggests.
[tex]5z+3x+7x=105[/tex]
[tex]15x=105[/tex]
[tex]x=7[/tex]
Then we can plug back in to find the numbers.
[tex]5*7=35[/tex]
[tex]3*7=21[/tex]
[tex]7*7=49[/tex]
[tex]35+21+49=105[/tex]
The three numbers are [tex]35, 21, 49[/tex].
Hope this helps.
頑張って!
