Perform the indicated operation with signed decimals: $-5\mathrm{.}7+2\mathrm{.}4(-6\mathrm{.}8+3\mathrm{.}9)$

Select one:

a$.-12\mathrm{.}66$

b$.12\mathrm{.}66$

c$.+23\mathrm{.}49$

d$.-31\mathrm{.}38$