A navigator on a boat measures the angle between the course of the boat and the lighthouse on shore to be 70 degrees. After the boat has traveled 3000 m, the navigator measure the angle to be 100 degrees. How far, to the nearest metre, was the boat from the lighthouse at the time of the first sighting?

hi pls where can I get physics questions on checking the correctness of an equation using dimensional analysis

5=812a+9+3

step 1: simplify both sides of the equation.

5=812a+9+3

5=(812a)+(9+3)(combine like terms)

5=812a+12

5=812a+12

step 2: flip the equation.

812a+12=5

step 3: subtract 12 from both sides.

812a+12−12=5−12

812a=−7

step 4: divide both sides by 812.

812a /812 = -7/812

a= -1/116

so the answer is

a=   -1/116