Maths Question~!!!好急

let Sarah's age = x
so "three years" later
Sarah (S): x+3
Sarah's Mother (M): 3(x+3)
Sarah's Father (F): 3(x+3) + 5

now:
S: x
M: 3(x+3) - 3 = 3x + 6
F: 3(x+3) + 5 - 3 = 3x + 11

total: x + (3x+6) + (3x+11) = 80
7x + 17 = 80
x = 9

Let the current age of Sarah be x, Sarah's mother be y and Sarah's father be (y+5)
{ x+3=(y+3)/3→(1)
x+y+(y+5)=80→(2)

If use the substitution method:
From (1), Sub(3)into(2), Sub y=33 into(3)
x+3=(y+3)/3 x+y+(y+5)=80 x=y/3-2
x+3=y/3+1 y/3-2+y+y+5=80 x=33/3-2
x=y/3+1-3 y/3+2y+3=80 x=9
x=y/3-2→(3) 7y/3=80-3
3(7y/3)=77(3)
7y=231
y=33
̣˙.The current age of Sarah is 9 years old.

If use the elimination method,
(1)-(2) Sub y=33 into(1),
x+3-x-y-(y+5)=(y+3)/3-80 x+3=(y+3)/3
3-y-y-5=y/3+1-80 x+3=(33+3)/3
-2y-y/3= -79+2 x=12-3
-7y/3= -77 x=9
3(-7y/3)= -77(3)
-7y= -231
y=33
̣˙.The current age of Sarah is 9 years old.

Hope I can help you.