Problem solving

Question

the averag of x,y,z is 80.If two of the numbers are 74 and 78,then what is the other number?

 

pls can someone explain that

Answer 1

the average = sum of the items÷the number of items

 

so, (x+y+z)/3=80

 

or,

 

(74+78+x)/3=80

 

solve for x