Question

if y:18 = 8:y, calculate the positive value of y

Answer 1

y:18=8:y
y×y=18×8
y×y=144
y=12

Answer 2

a:b=c:d
ad=bc
y:18=8:y

y*y=18*8
y^2=144
y^2=(12)^2
therefore
y=12