
Let

, and recall that in polar coordinates,

. This means you have

You can stop there, or try to find something that looks somewhat nicer.
Answer: x=7.5
Step-by-step explanation:
7 is the radius of the circle
5(1)= 5; identity property of multiplication
(3+5)+0=(3+5); identity property of addition
[3(5)](4)=(3)[5(4)]; associative property of multiplication
3+5=5+3; commutative property of addition
3+(5+7)=(3+5)+7; associative property for addition
hope this helps :)