Got a fairly simple looking system of equations, 2k+4y=20, and 3x+6y=30 Don't understand how to prove what values of k provide - 1 solution - no solutions - and many solutions

I’m really confused and need to learn this

You have 37 coins that are nickels, dimes, and pennies. the total value of the coins is $1.55. there are twice as many pennies as dimes. find the number of each type of coin in the bank.

Amayoral candidate would like to know her residents’ views on a tax on sugar drinks before the mayoral debates. she asks one thousand registered voters from both parties. these voters are an example of a census population convenience sample simple random sample