I need help! 6th grade math! ASAP! Only 1 and 3. 10 Points each!

What is the value of m in the equation 1/2 m - 3/4n=16 when n=8

Look at the figure below: triangle abc is a right triangle with angle abc equal to 90 degrees. the length of ac is 5 units and the length of ab is 4 units. d is a point above c. triangle adc is a right triangle with angle dac equal to 90 degrees and dc parallel to ab. what is the length, in units, of segment cd?

Which of the following circles have their centers in the third quadrant?