7x+5y=-24 (1)
4x+y=42 (2)
multiply equation (2) by 5 to get
20x+5y=210 (3)
then calculate (3)-(2) which gives you
13x=234 hence x=18
then substitute for x in either equation to get y=-30
You could use many methods to find the answer to this problem, but I am going to use the most efficient one I know.
18f+15(4f)=156
F is for fins. We should now solve the equation.
18f+60f=156
78f=156
156÷78=2
So fins cost 2 dollars. Now, we know snorkels cost four times the amount of fins. Four times 2 is eight. So the snorkels cost $8 to rent. Let's check our math.
15(8) + 18(2)
120+36=156
So it cost $8 to rent a snorkel.
