If a cell has 18 chromosomes and undergoes mitosis, how many chromosomes would each daughter cell have?

Each daughter cells will have 18 chromosomes. Mitosis is the type of cell division in which the parent cell divides to yield offsprings which have the same number of chromosomes as the parents. The process takes place in the somatic cells or the body cells, unlike meiosis, the diploid cells yields two diploid daughter cells after division. 

Each daughter cell will also have 18 chromosomes.
The purpose of mitosis is to make more same diploid daughter cells. Mitosis involves copying of each chromosome and then separating the copies to different sides of the cell. That way, when the cell divides each new cell gets its own copy of each chromosome (the same number as mother cell).