Could you explain how you got the answer to please

If a =6, what is the value of 2a(3b + 5c)?

Explain step-by-step how to simplify -5(2x – 3y + 6z – 10).

Arley is building a model of a city map. in one part of the city, three roads form a right triangle, which harley draws as triangle abc, with the following measures: m∠b=90° and m∠a=30°. in his scale model, the hypotenuse of triangle abc, ac¯¯¯¯¯¯¯¯, has a length of 817−−√ cm. what is the value of a (the length of bc¯¯¯¯¯¯¯¯)?