How many columns and rows are defined in the following code?
section {
display: grid;
grid-template-columns: 100px 1fr 1fr 250px;
grid-rows: 50px 1fr 1fr ;
}

section header {
grid-column: 1 / 4;
grid-row: 1;
}

section nav {
grid-column: 1;
grid-row: 2 / 3;
}

section article {
grid-column: 2;
grid-row: 2;
}

section aside {
grid-column: 3;
grid-row: 2;
}

section footer {
grid-column: 1 / 4;
grid-row: 3;
}