Solve the proportion 12 / 30 = x / 5 What is the value of x

If you look for the equivalent values, in this case the 'bottom number' you can find what it has been multiplied/divided by.

Here we have 30 -> 5 which means it's been divided by 6
Do the same to the other value
12/6 = 2

so x = 2

cross multiply: (12)(5) = 30x
60 = 30x

divide by 30 so
x = 2

60 / 30 = x

x = 2