well first, you should always start with multiplication( if the dot meant multiplication)
so, multiply 10 with 64= 640
and then multiply 8 with 8= 64
and then subtract them together, you'll get 574
but, if the dot meant "decimal"
and then write it horizontally, the 10.64 on top and then the 8.8 on the bottom
start subtracting from the right side to the left, you'll get : 1.84