Two mechanics worked on a car. the first mechanic worked for 20 hours, and the second mechanic worked for 5 hours. together they charged a total of $1900 . what was the rate charged per hour by each mechanic if the sum of the two rates was $155 per hour?

20x + 5y = 1900
x + y = 155multiply by -20

20x + 5y = 1900
-20x - 20y = - 3100 (result of multiplying by -20)
add
-15y = -1200
y = -1200/-15
y = 80 <== 80 per hr for the mechanic that worked 5 hrs

x + y = 155
x + 80 = 155
x = 155 - 80
x = 75 <== 75 per hr for the mechanic that worked 20 hrs

One unique triangle, because those angles add up to 180, and that's how many degrees there are in one triangle.