selma is now 3 times older than joyce. four years ago, selma was 4 times as old as joyce was then. find their present ages

Present age of Selma = s

Present age of Joyce = j

Selma is now 3 times as old as joyce

s=3j ... (1)

Four years ago,

s-4=j-4

then

Selma was 4 times as old as joyce

s-4=4 (j-4)

s-4=4j-16

s=4j-16+4

s=4j-12 ... (2)

Put the value of s in (2) from (1)

3j=4j-12

3j-4j=-12

-j=-12

Multiply by - 1 both sides

j=12

Put the value of j in (1)

s=3j

s=3 (12)

s=36

Present age of Selma = s = 36 years old

Present age of Joyce = j = 12 years old