Detecting in view entity's

Help Requests
1

So in my game (With a plants vs zombies style) my towers are placed in rows, and the enemy’s walk on these rows too. Right now I have it so my towers attack if an enemy is on screen at all. But I want to change it to reduce lag, so that they only fire if the enemy’s are in the same row

Does anyone know how to detect that?

2

Why not have your towers send a raycast before they attack, and skip the attack unless the ray hits an enemy?

3

Thank you so much, I never knew how to use Ray-Cast