The area under the standard normal curve for a given `z` value can be found by consulting the `z-` table or using technology. The number in the table represents the area under the curve to the left of the given `z` value.
Thus if `z=.87` , the area under the standard normal curve to the left of `z=.87` is approximately .8078. If the picture you are looking at has the area to the right of `z=.87` , then the area is 1-(the area to the left), or in this case approximately 1-.8078=.1922.
Consulting a graphing calculator (TI-83), I used distr -- normalcdf(-e99,.87) to get .8078498426.