A fraction is usually split into two parts: the first part is the number on top, called the numerator; and the second part is the number on the bottom, called the denominator. These are both separated by a line called the “divisor line”. We can use the division method help to solve this question: to get a decimal, simply divide the numerator 87 by the denominator 17 (which you can enter in any calculator):
87 (numerator) ÷ 17 (denominator) = 5.12
And finally, you get 5.12 as your answer when you convert 1 70/17 (or 87/17) to a decimal.