The number of stamps with penny in terms of x is 
<em><u>Solution:</u></em>
Given that,
Ryan has x stamps in his collection
Number of stamps of Ryan = x stamps
Let the stamps with penny be "a"
Ryan has 6 times as many stamps as penny
Therefore,
Number of stamps in Ryan = 6 times as many stamps as penny

Thus number of stamps with penny in terms of x is 
Answer:
3
Step-by-step explanation:
0.75 x ? = 15
? = 15/0.75 = 20
15% of 20 = 3
Answer:

Step-by-step explanation:
Given that,
The frequency of x-rays, 
We need to find the wavelength for x-rays. The relation between wavelength, frequency and speed of light is given by :

So, the wavelength for x-rays is
.