Matt needs to buy new plates for his home.  He only wants to do dishes once a week.  Three days a week it is only him and his son eating and they use 1 plate each.  On the remainder of the days, his parents join them and everyone uses 2 plates that day.  How many plates does he need to buy?
So for 3 of the days, there are 1+1=2 people eating
So for those days they use 3*2=<<3*2=6>>6 plates
On 7-3=4 days the parents join them
On those days there are 2+2=<<2+2=4>>4 people eating
They use 4*2=<<4*2=8>>8 plates
So they use 8*4=<<8*4=32>>32 plates
That means they use a total of 32+6=<<32+6=38>>38 plates
#### 38