This problem is about the rule of three, where we have the given ratio "1 inch wide to 4 inches tall", based on this ratio we can find the inches tall for 3 inches wide.
So, we just need to form an equation, where the given ratio is going to form a fraction, we must multiply the "3 inches of width".
[tex]x=3in(width)\cdot\frac{4in(\text{tall)}}{1in(width)}[/tex]Then, we multiply:
[tex]x=12in(tall)[/tex]