Let 'x' be the age of Cita at present
'y' be the age of Bona at present
'z' be the age of Albert at present
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Four years from now:
x+4 ---Cita's age
y+4 ---Bona's age
z+4 ---Albert's age
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Translating the statements into mathematical expressions you'll have:
x = y + 6 ----equation 1
y = 2z ----equation 2
(x+4) = (y+4) +(z+4) - 8 -----equation 3
From equation 3
(x+4) = (y+4) +(z+4) - 8
x + 4 = y + 4 + z + 4 - 8
x + 4 = y + z -----equation 3'
Express x and z in terms of y
From equation 2
y = 2z
z = y/2 ----equation 2'
Substitute equations 2' and equation 1 to equation 3'
x + 4 = y + z
(y+6) + 4 = y + y/2
y + 6 + 4 = y + y/2
Combine like terms
y - y + y/2 = 10
y/2 = 10
Cross multiply
y = 20 yrs old ----Bona's age
Substitute y=20 to equation 2
y = 2z
20 = 2z
z = 20/2
z = 10 ----Albert's age
substitute y=20 to equation 1
x = y + 6
x = 20 + 6
x = 26 yrs old ---Cita's age
