A trapezoid has parallel sides of lengths 10 and 15; its two other sides have lengths 3 and 4. Find the area.
Try here (and see explanation of equation in lower R)
https://owlcalculator.com/Geometry/Area/Trapezoid-Area/By-lateral-sides-and-bases
what is the formula
the site is blocked on my computer I really want to know it.