Let's write T for Teagan's score and E for Emma's score.
Also, let's write an equation
E = 2T + 4
E = 3
2T + 4 = 3
subtract 4 from both sides
2T = -1
divide both sides by 2
T = -1/2
To see of this is correct:
2T + 4 = 3
2(-1/2) + 4 =?= 3
-1 + 4 =?= 3
3 = 3
Hope this helps