in the method of borrowing, a subtraction such as will accomplish the ones-place subtraction of 9 from 6 by borrowing a 10 from 80 and adding it to the 6. the problem is thus transformed into effectively. this is indicated by striking through the 8, writing a small 7 above it, and writing a small 1 above the 6. these markings are called "crutches". the 9 is then subtracted from 16, leaving 7, and the 30 from the 70, leaving 40, or 47 as the result.