5c-9=8-2c and if not asking too much explain how you got the answer

d. 145*2 is 290 than the total angle is 360 then minus 290 then divide by two

answer: 4  

the square root of 16 is 4. it is a very simple mathematic concept. a square root when a number multiplied by itself will result in a number. here, the number 16 comes when 4 is multiplied by 4. hence the square root of 16 is 4. you can always figure out a square root by the inverse operation of squaring.