simplifying algebraic equations

Area​=3⋅2h(−6)+h(−3)​+3⋅2h(−3)+h(0)​+3⋅2h(0)+h(3)​+3⋅2h(3)+h(6)​=23

          ​[h(−6)+2⋅h(−3)+2⋅h(0)+2⋅h(3)+h(6)]=

          23​(0+2⋅5+2⋅3+2⋅5+0)=39​

Hi, I'm stuck on how to simplify the first Eq. down to the second Eq. and the second down to the third. h(x) above from a function to determine the Y component for use in calculating the area of a trapezoid. Thanks, jim