Answer:
El area del trapecio mresponde a la relación
           A = 1/2(B + b)*h
             B = base mayor
              b = bas menor
              h = altura
En el caso en esrudio
                       250 = 1/2(B + 20)*10
                   2*250/10 = B + 20
                        50 = B + 20
                    50 - 20 = B
                         B = 30
                                BASE MAYOR = 30 PIES
