Variables and Algebraic Expressions: Complete the missing numbers

$(a+8)(b+7)-▭=7a+8b$

$▭=\text{?}$

$ab+56$

Fill in the blank:

^{$9a+8b+7c+_—bc=9a+12b+7c$}

$\frac{4}{c}$

$△+6.1x+7.4y+☐=4.7x-0.4y$

What values are possible for ☐ and △ so that the equation can be satisfied?

a. $\triangle=-7y$
$☐=-1.4x$

b. $△=-7.8y$

$☐=-1.4x$

c. $△=-1.4x$

$☐=-7.8y$

d. $△=-3.4x$

$☐=-7.8y+2x$

b, c, d

Fill in the gap so that the equation is satisfied:

^{$\frac{2}{5}a+\frac{3}{4}ab+\frac{2}{3}b=_—a+\frac{1}{3}b+\frac{1}{3}b$}

$$$\frac{2}{5}+\frac{3}{4}b$

$2x(\frac{2}{3}x+\frac{4}{7}y)+\frac{6}{7}x(4+☐)=1\frac{1}{3}x^2+3\frac{3}{7}x+2xy$

$☐=\text{?}$

$y$

^{$y(?)+\frac{2}{3}(x+y)=\frac{2}{3}x+2\frac{8}{9}y+5xy$}

$2\frac{2}{9}+5x$