\(x=19\)

a)dien h xung quanh cua hinh do la:

(5+4)*2*3=54 (cm2)

b)dien h xung quanh cua hinh do la

(3+4)*2*5=70(cm2)

d/s:a)54 cm2

      b)70 cm2

x + 10 = 90

x          = 90 - 10

x          = 80.

\(\frac{10}{15}\)=\(\frac{2}{3}\)

\(\frac{12}{16}\)=\(\frac{3}{4}\)

QUY ĐỒNG:\(\frac{2}{3}\)và\(\frac{3}{4}\)thành

\(\frac{8}{12}\)và\(\frac{9}{12}\)

400 nhé