If Johnnie earns $7 for every yard he mows and he mows at least 16 yards, we can calculate the minimum amount he would earn.
For 16 yards, the calculation would be: \[ 16 \text{ yards} \times 7 \text{ dollars/yard} = 112 \text{ dollars} \]
So, if Johnnie mowed at least 16 yards, he would have at least $112 in his account. If he mowed more yards, the amount would increase accordingly.