Marked price of an article is Rs. 2,500 which is Rs. 900

Find the unknown value of' x' in the proportion $$(5x + 1) : 3 = (x + 3) : 7

√1936 + √3025 = ? % of  220

If (7a + b) : (7a - b) = 7:3, then find the value of  a:b?

What should come in place of the question mark (?) in the following question?

2 – [6 – {3 + (–4 + 5 + 1) × 8} + 12] = ?

255 × 8 + 386 × 5 =? % of 7940

 (5/8) × 480 + (3/9) × 450 = (5/2) × ?

The value of 0.0486 ÷ 0.002 = 

0.25 x 696 ÷ 0.3 = ?

125% of 129 ÷ 43 × 28 ÷ 7 = ? ÷ √16

Find the simplified value of the given expression:

1.8² + 2.4² + 1.5² - 1.8 x 2.4 - 2.4 x 1.5 - 1.8 x 1.5