A factory has two assembly lines, $M$ and $N$, that make the same toy. On Monday, only assembly line $M$ was functioning, and it made 900 toys.

On Tuesday, both assembly lines were functioning for the same amount of time. Line $M$ made $300$ toys per hour and line ${N}$ made $480$ toys per hour. Line ${N}$ made as many toys on Tuesday as line ${M}$ did over both days.

Write an equation that can be used to find the number of hours, $t$, that the assembly lines were functioning on Tuesday.