To graph the two functions, set arbitrary functions of x. As you set different values of x, you get their corresponding values of y. When you have both coordinates, you plot them as shown in the picture. The blue line represents the function f(x) = 3x, while the orange line represents the function f(x) = -x+4.
Indeed, the two lines intersect at point (1,3). To solve this analytically, set the system of equations:
y = 3x
y = -x + 4
Equating both equation of y,
3x = -x + 4
4x = 4
x = 1
Then, use any of the original equations: y = 3x = 3(1) = 3. Hence, the solution is (1,3). What does this solution mean? It means that when temperature is at 3 units, the people leaving and entering the small zoo are equal. Meaning, for every 1 person that comes in, another 1 leaves.
Indeed, the two lines intersect at point (1,3). To solve this analytically, set the system of equations:
y = 3x
y = -x + 4
Equating both equation of y,
3x = -x + 4
4x = 4
x = 1
Then, use any of the original equations: y = 3x = 3(1) = 3. Hence, the solution is (1,3). What does this solution mean? It means that when temperature is at 3 units, the people leaving and entering the small zoo are equal. Meaning, for every 1 person that comes in, another 1 leaves.