2s-2=7
2s=9
s=4.5
3*4.5*5t=10
13.5*5t=10
5t=10/13.5
5t=0.74
t=0.148
$${\mathtt{0.5}}{\mathtt{\,\times\,}}{\mathtt{4.5}}{\mathtt{\,\small\textbf+\,}}{\mathtt{3}}{\mathtt{\,\times\,}}{\mathtt{0.148}} = {\frac{{\mathtt{1\,347}}}{{\mathtt{500}}}} = {\mathtt{2.694}}$$
.