## Help with simple microeconomic problems

I'd appreciate any help on these problems. I'm interested in understanding how to solve it rather than the solution.

1.) Charlie’s utility function is xy. The price of x used to be $1, the price of y used to be$2, and his income used to be $40. If the price of x increased to$5 and the price of y stayed constant, the substitution effect on Charlie’s x consumption would reduce his consumption by:

2.) Cindy consumes goods x and y. Her demand for x is given by x(px,m) = .05m - 5.15p where px is price of x and m is income. M is 419, the price of x is 3 and the price of y is 1. If the price of x rises to \$4 and if we denote the income effect on her demand for x by DI and the substitution effect for her demand for x by DS, then what are the values for DI and DS/

3.) Ernest's income elasticity of demand for natural gas is 0.4. His price elasticity of demand for natural gas is -0.3 and he spends 10% of his income on natural gas. What is his substitution price elasticity?