I need help solving for x please

What number should be added to both sides of the equation to complete this square? x^2-10x=7

Measures of the angle of r, 31 s (x+4) t (3x+9)

Tod does not have any cookies. david gives jeff 8 cookies. then he splits half of the cookies he has left with tod. david let’s c represent the number of cookies that he starts with. he finds the number of cookies that tod has is 1/2 the difference of c and 8. write an expression to represent the number of cookies that tod has.