A school is organizing a fundraising event through the sale of tickets for a concert. The cost of each adult ticket is $15, and the cost of each child ticket is $10. The school aims to raise at least $1500 from ticket sales. If the school expects to sell three times as many child tickets as adult tickets, let x be the number of adult tickets sold.

How many total tickets must be sold to meet the fundraising goal, expressed as a single number in grid-in format?

Use the following equations to model the situation:

The number of child tickets sold:
$$3x$$

The total revenue from ticket sales:
$$15x + 10(3x) ext{ must be greater than or equal to } 1500$$