To find out how many jazz dance classes Christina has taken, you can set up a ratio based on the information given:
7 jazz dance classes / 2 ballet classes = X jazz dance classes / 24 ballet classes
Now, you can cross-multiply and solve for X:
7 * 24 = 2 * X
168 = 2X
Now, divide both sides by 2:
X = 168 / 2
X = 84
So, Christina has taken 84 jazz dance classes this year.