Question

Assign two variables for each problem, and write the equations. Solve.

Answer 1

Lets make k equal to Kate's age and j equal to Joey's age.  If in 5 years Kate will be twice as old as Joe, you can write the equation k+5=2(j+5) and then simplify it to make it easier to work with.
k+5=2(j+5)
k+5=2j+10
k+5-2j=10
k-2j=5
since we know that right know Kate is 11 years older than Joey, you can write the equation k+j=11.  Since you know have two equations with with the same variable, you can make a system of equations as fallows:
k-2j=5
k+j=11

Since you need to figure out how old Joey is, you need to somehow get k to cancel out.  The easiest thing to do for this problem is to is multiply the top equation by -1 to get:
-k+2j=-5   (you have to add the bottom equation to the top equation)
k+j=11     (-k+k=0, 2j+j=3j, and -5+11=6)
Since k got canceled out, you are left with the equation 3j=6 which means j=2.
Therefore, Joey's current age is 2.

I hope this helps.