This is a Ratio and Proportion problem.
Here is one way to solve this problem.
Set up a series of equations that show the ratios, then solve for #x#.
#(x)/(y) = (12)/(8) = (x)/(12)#
#Note:# Always set up a word fraction first because the most common error is accidentally swapping the entries for the numerator and denominator.
1) Cross multiply
#8x = 144#
2) Divide both sides by #8# to isolate #x#
#x = 18# #larr# answer
Check
Sub in #18# for #x# to be sure the fractions are still equal.
#(x)/(y) = (12)/(8) = (18)/(12)#
Cross multiply
#(8)(18)# should equal #(12)(12)#
#144# does equal #144#
#Check#
Here's another way to check.
#(x)/(y) = (12)/(8) = (x)/(12)#
Sub in #18# to be sure the fractions are still equal.
#(x)/(y) = (12)/(8) = (18)/(12)#
Instead of cross multiplying, reduce each fraction to lowest terms to see if they are still equal
Reduce the first fraction by #4# and the second fraction by #6#
#(x)/(y) = (3)/(2) = (3)/(2)#
#Check#
