Chapter 7 - Section 7.2 - Proportion - Exercises - Page 277: 41

x=21.3

Set the product of the means equal to the product of the extremes and solve for the variable. $4.2\times19.6=x \times 3.87$ $82.32=3.87x$ $82.32\div3.87=3.87x\div3.87$ $21.\underset\uparrow271=x$ Since the digit to the right of the 3rd significant digit is greater than 5, round up.