Respuesta :

Answer: y = 3 or y=7

Step-by-step explanation:

[tex]y^{2} -10y+21[/tex]

what 2 factors of 21 can equal 10 when added together (1*21- no 3*7- yes)

Factor

[tex](y-3)(y-7)[/tex]

y-3=0

y=3

or y-7=0

y=7