Let the number of hours = x
Mine A is offering his services for an initial $90 in addition to $15 per hour.
So, Charges of A = 90 + 15x
Mine B is offering her services for an initial $30 in addition to $35 per hour.
so, Charges of B = 30 + 35x
The two mines charge the same amount of money when:
Charges of A = Charges of B
So,
solve for x
combine like terms
so, the two mines will charge the same amount of money when the number of hours = 3