C hope it helps .....................
Let x represent the amount to be added. The total amount of tin will be
15%·20 + 10%·x = 12%·(20+x)
(15%-12%)·20 = (12%-10%)·x
3%·20/2% = x
30 = x
30 pounds of 10% tin must be added to get a 12% mixture.
Answer:
Distance between the police station and the fire station be 4 miles
Step-by-step explanation:
Let distance between the police station and the fire station be x miles.
The distance between the library and the police station is 3 miles less than twice the distance between the police station and the fire station.
Distance between the library and the police station 
Also, distance between the library and the police station is 5 miles.

3-3 x 6+2= -13
The answer= -13
Step-by-step explanation:
Put 1 on the far left and 4 on the far right.
Put. 2 the top and 3 at the bottom.
Put 5 in the centre.
There are 2 ways you can find to to make all the numbers add up to 5.
The number in the centre is the common anwser to the sums.