Answer:To find out how much more Cristina needs to buy the shoes for her sister,we can subtract the amount she already saved from the total cost of the shoes.Given:•Amount Cristina already saved:PHP 555.50•Cost of the shoes:PHP 1465.75To calculate how much more Cristina needs to buy the shoes:Total cost of the shoes-Amount she already saved=Amount still neededSoPHP 1465.75-555.50=PHP 910.25Cristina still needs PHP 910.25 to buy the shoes for her sister as a birthday gift.