(1) indicates the range of (x, y) values defined by each constraint in turn. Specifically, draw a straight line with the unequal sign as the equal sign, and then determine whether it is "above" or "below" and whether the package contains that line. If "up" and "down" are not clear, substitute a set of (x, y) that satisfy the inequality and see which side it is on. In this way, the range of (x, y) is obtained.

(2) Then look at the Z expression that needs extreme value. Draw a straight line with z as 0 first. Then choose one of x and y to observe. For example, if we look at X here and find that z=2x+3y ignores Y, then Z decreases with the decrease of X, that is, the parallel movement of 0=2x+3y to the left (negative direction of X axis) corresponds to a smaller Z value. It is easy to see (you can draw a line with a ruler) that the farthest movement can intersect with the area obtained by (1), which is usually the intersection point of the straight line of one of the above two constraints, and then substitute the intersection point into the expression of z, and the minimum value of z can be obtained by combining two equations.