J+J+E=42
In this case, the substitution method would be a lot easier than elimination.
Substitution (J*1/3) in for E into the second equation and solve for J.
J+j+j*1/3=42
Multiply by 3 to get rid of the fraction
3J+3j+j=126
7j=126
J=18
Now that you know j, u can plug that back into the first equation.
E=18*1/3
So you were right. 18 for the twins and 6 for Emily.
Problem two: there isn't enough info to tell how many Katy got right, but I can te u how many were on the teast.
X=number of 2 point problems
Y=number of three point problem
Equation 1:
2x+3y=100
Equation 2:
X+y=42
If you substitute just like last time:
X+y=42 so y=42-x
The variable cross each other out and:
42=42
The answer J's I.finite number of solutions.