Answer:
9 weeks
Step-by-step explanation:
let the time when they will both have the same amount be x
since Maria is saving then her money is bound to increase
therefore amount she will have after x weeks=235+15x
Sergio is spending so his money is reducing
therefore amount he will have after x weeks=
685-35x
so
235+15x=685-35x
685-235=15x+35x
450=50x
x= 450/50
9weeks