Let's turn that into a linear system:
[tex] \left \{ {{y=0.05x+20} \atop {y=0.25x+10}} \right. [/tex]
Set the equations equal to each other and solve:
[tex]$0.05x+20=0.25x+10$[/tex]
[tex]$0.2x=10$[/tex]
[tex]$x=50$[/tex]
We then plug in to get [tex]$y$[/tex]:
[tex]$0.25(50)+10=22.5$[/tex]
The solution to the system is [tex] \left \{ {{x=50} \atop {y=22.5}} \right. [/tex].
Now, let's turn our attention to the statements.
The first one is false: Emilia's rate is higher, and the two plans cost the same at 50 texts, after which point Hiroto's plan becomes cheaper!
The second one is also false: we already figured out that the lines intersect at [tex]$x=50$[/tex].
The third statement is also false: as above, the lines intersect at [tex]$x=50$[/tex].
The fourth statement is true: the lines intersect at [tex]$x=50$[/tex].
In conclusion, the fourth statement - "Both plans cost the same when 50 texts are sent" - is true.
