Darwin's best time for running 5000 metres is 16 minutes. He wants to run it in 15 minutes and 30 seconds. What percentage reduction in time is this?

Please include explanation! ​

If m∠abc = 70°, what is m∠abd? justify your reasoning.  using the addition property of equality, 40 + 70 = 110, so m∠abd = 110°.  using the subtraction property of equality, 70 − 30 = 40, so m∠abd = 30°.  using the angle addition postulate, 40 + m∠abd = 70. so, m∠abd = 30° using the subtraction property of equality.  using the angle addition postulate, 40 + 70 = m∠abd. so, m∠abd = 110° using the addition property of equality.

Precalculus question, image attached.

Solve the equation for b: a= (1/2)(b)(h)