Dorothy is 10 years older then her brother. if the product of their ages is 231, how old is dorothy?

D * b = 231
d = b + 10

b(b + 10) = 231
b^2 + 10b = 231
b^2 + 10b - 231 = 0
(b - 11)(b + 21) = 0

b - 11 = 0
b = 11 <== brothers age

b + 21 = 0
b = -21extraneous solution...does not work

d = b + 10
d = 11 + 10
d = 21 <== dorothy's age

so dorothy is 21 and her brother is 11

Ibelieve 4mn because it’s like you’re combining them