Question 1. question 2. and question 3. Thanks! :)
The periodicity of function is 
<em><u>Solution:</u></em>
Given that we have to find the period of function
<em><u>Given function is:</u></em>

<em><u>Use the below formula:</u></em>

Thus,

Now find the periodicity of cos(x)
We know that,
periodicity of cos(x) = 
Therefore,

Thus the periodicity of function is 
To get p add 18 on both side then you will get 56 as p which is the answer
In 8 years, you will have $1,573.29 thus $850-$1573.29 = $ <span>723.29 in interest</span>