Solve the following simultaneous equations using an appropriate method.
a) 2x + y = 8
4x + 3y = 16
b) -3x + 2y = 19
4x + 5y = 13
c) -3x + 7y = 9
4x - 3y = 7
d) -4x + 5y = -7
x = 23 - 3y

Starting at home, emily traveled uphill to the hardware store for 606060 minutes at just 666 mph. she then traveled back home along the same path downhill at a speed of 121212 mph. what is her average speed for the entire trip from home to the hardware store and back?