Combine the like terms for the following equations:
7x + 4(2x - 6)
b² + 3 + 2b² +4 - 7
3m - 6 + m² - 5m + 1
3(p + 5) - 8 + 11p
requirements: explanation and answer for each one
reward: 20 points
good luck!

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?