The answer would be -105. If you multiply 7 x -15 it would give you -105 and then you would have to divide -105 by 7 and its equal to -15.
Find a common denominator between the two (this case it would be 18) and bring the fractions up, so 10/9 would be 20/18, and 3/2 would be 27/18. Then, multiply across, and simplify to lowest terms.
y = total cost used.
x = additional minutes
y = $49.95 + $0.15x
$61.20 = $49.95 + $0.15x. Subtract the $49.95 from each side.
$11.25 = $0.15x. Divide each side by $0.15
75 = x.
Michael used 75 additional minutes.