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?