脱式计算（能简算的要简算）．

① $\frac{4}{5}-\frac{8}{5}÷\frac{5}{6}$              ② $\frac{7}{5}-\frac{2}{5}÷\frac{7}{15}-\frac{1}{7}$

③0.8×0.95+0.3×0.8       ④ $\frac{4}{15}\times (\frac{3}{4}-\frac{7}{12})÷\frac{4}{9}$ ．

赵州桥的主桥拱是圆弧形，它的跨度（弧所对的弦）长为37.4m，拱高（弧的中点到弦的距离）为7.2m，请求出赵州桥的主桥拱半径（结果保留小数点后一位）．

—I like the photo          I took on the beach yesterday. What do you think of it?                   
—Well, really nice!