Customers of a phone company can choose between two service plans for long distance calls. the first plan has an $18 monthly fee and charges an additional $0.14 for each minute of calls. the second plan has an $8 monthly fee and charges an additional $0.19 for each minute of calls. for how many minutes of calls will the costs of the two plans be equal?

check the picture below.

well, the angle at the vertex d is clearly not a right-angle, let's check for the one at the vertex f which does look like,   however if it's indeed, that means ef is perpendicular to df, in which case their slopes will be negative reciprocal of each other.

so the negative reciprocal of the slope of ef is 1, however the slope of df is not 1, is 1/2, so nope, they're not perpendicular lines.

i cant see the graph

step-by-step explanation: