Check whether the ratio forms a proportion: (Write the answer as 'Yes' or 'No')

$25:40 and 20:32$

Check whether the given ratio forms a proportion 

$\frac{15}{18} \text{and} \frac{10}{12}$

Check whether the ratio forms a proportion 

$\frac{7}{8} and 14:16$

Find the value of $x$

$x:4 = 6:8$

Find the value of $x$

$14:x = 7:9$

Find the value of $x$

$4:6 = x:18$

Find the value of $x$

$8:10 = x:25$

Find the value of $x$

$5:15 = 4:x$

Find the value of $x$

$16:24=6:x$