Cracked toilet tank, does leak

There is now a crack at the top of the toilet tank.It travels from the top edge in the front down and to the side. When the tank has water, it does leak.

[1] Is there a way to repair the crack? Can this be the simplest and best solution?

[2] Can we replace just the tank part?

[3] Do we have to replace the whole toilet?

Thanks for your help.